The E3 ubiquitin ligase ITCH negatively regulates intercellular communication via gap junctions by targeting connexin43 for lysosomal degradation.

Intercellular communication via gap junctions has a fundamental role in regulating cell growth and tissue homeostasis, and its dysregulation may be involved in cancer development and radio- and chemotherapy resistance. Connexin43 (Cx43) is the most ubiquitously expressed gap junction channel protein in human tissues. Emerging evidence indicates that dysregulation of the sorting of Cx43 to lysosomes is important in mediating the loss of Cx43-based gap junctions in cancer cells. However, the molecular basis underlying this process is currently poorly understood. Here, we identified the E3 ubiquitin ligase ITCH as a novel regulator of intercellular communication via gap junctions. We demonstrate that ITCH promotes loss of gap junctions in cervical cancer cells, which is associated with increased degradation of Cx43 in lysosomes. The data further indicate that ITCH interacts with and regulates Cx43 ubiquitination and that the ITCH-induced loss of Cx43-based gap junctions requires its catalytic HECT (homologous to E6-AP C-terminus) domain. The data also suggest that the ability of ITCH to efficiently promote loss of Cx43-based gap junctions and degradation of Cx43 depends on a functional PY (PPXY) motif in the C-terminal tail of Cx43. Together, these data provide new insights into the molecular basis underlying the degradation of Cx43 and have implications for the understanding of how intercellular communication via gap junctions is lost during cancer development.

CD98hc as a marker of radiotherapy-resistant cancer stem cells in head and neck squamous cell carcinoma.

Introduction: The prognosis of head and neck squamous cell carcinoma (HNSCC) is generally good in cases of high radiation sensitivity but poor in cases exhibiting radiation resistance; this resistance has been attributed to the presence of cancer stem cells. In recent years, CD98hc overexpression has been associated with poor prognosis in various types of cancers. CD98 is a heterodimer of heavy and light chains and is strongly involved in cell proliferation, survival, migration, and adhesion. We investigated whether CD98hc can be used as a cancer stem cell marker for HNSCC. Material and methods: We exposed five HNSCC cell lines to a total radiation dose of 60 Gy administered in 2 Gy fractions on consecutive days to investigate changes in CD98hc expression. Furthermore, we separated CD98-positive and CD98-negative cell populations to comparatively investigate the properties of each. Results: Radiation resistance was observed in all five cell lines, and resistant cells exhibited CD98hc overexpression, with enhanced spheroid formation, migratory, and invasive abilities. Radiation-resistant cell lines were separated into CD98-positive and CD98-negative populations. CD98hc-positive radiation-resistant cell lines exhibited enhanced spheroid formation, invasion, and plating efficiency as well as strong tumorigenicity in nude mice. Conclusions: CD98hc-positive cells exhibited cancer stem cell-like properties in all cell lines. Thus, CD98hc is a potential marker of radiation sensitivity as well as a potential therapeutic target for improved survival rates of patients with HNSCC.

CD98 expression can be a predictive factor of resistance to radiotherapy in head and neck squamous cell carcinoma.

CD98 is a marker of cancer stem cells, and it regulates radiosensitivity in head and neck squamous cell carcinoma (HNSCC). The current study aimed to investigate whether CD98 can be used as a prognostic factor and marker of radioresistance. CD98 immunostaining was performed using biopsy specimens collected from patients diagnosed with HNSCC. The average period of postoperative monitoring was 31.6 months. The treatment options were radiation therapy with either cisplatin or cetuximab, and surgery. The participants were divided into groups of low and high fluorescence intensity. CD98 was an independent prognostic factor of radioresistance. In total, 103 patients were treated with chemoradiotherapy or bioradiotherapy. The overall survival rates of patients receiving chemoradiotherapy or bioradiotherapy were 69.2% in the low group and 36.2% in the high group. The progression-free survival rates were 60.0% and 24.6%, respectively. CD98 expression was considered an independent prognostic factor of overall survival and progression-free survival. In total, 99 patients underwent surgical treatment. The surgery group did not differ according to CD98 expression. Via CD98 immunostaining, sensitivity to radiotherapy can be determined in advance. In HNSCC, knowledge about sensitivity to radiotherapy can significantly improve prognosis.

Endocytic trafficking of connexins in cancer pathogenesis.

Gap junctions are specialized regions of the plasma membrane containing clusters of channels that provide for the diffusion of ions and small molecules between adjacent cells. A fundamental role of gap junctions is to coordinate the functions of cells in tissues. Cancer pathogenesis is usually associated with loss of intercellular communication mediated by gap junctions, which may affect tumor growth and the response to radio- and chemotherapy. Gap junction channels consist of integral membrane proteins termed connexins. In addition to their canonical roles in cell-cell communication, connexins modulate a range of signal transduction pathways via interactions with proteins such as ß-catenin, c-Src, and PTEN. Consequently, connexins can regulate cellular processes such as cell growth, migration, and differentiation through both channel-dependent and independent mechanisms. Gap junctions are dynamic plasma membrane entities, and by modulating the rate at which connexins undergo endocytosis and sorting to lysosomes for degradation, cells can rapidly adjust the level of gap junctions in response to alterations in the intracellular or extracellular milieu. Current experimental evidence indicates that aberrant trafficking of connexins in the endocytic system is intrinsically involved in mediating the loss of gap junctions during carcinogenesis. This review highlights the role played by the endocytic system in controlling connexin degradation, and consequently gap junction levels, and discusses how dysregulation of these processes contributes to the loss of gap junctions during cancer development. We also discuss the therapeutic implications of aberrant endocytic trafficking of connexins in cancer cells.

LAT1 is associated with poor prognosis and radioresistance in head and neck squamous cell carcinoma.

Head and neck squamous cell carcinoma (HNSCC) has been identified as the sixth most common disease in the world, and its prognosis remains poor. The basic treatment of HNSCC includes a combination of chemoradiation and surgery. With the advent of immune checkpoint inhibitors, the prognosis has improved; however, the efficacy of checkpoint inhibitors is limited. L-type amino acid transporter 1 (LAT1), an amino acid transporter, is highly expressed in a cancer-specific manner. However, to the best of our knowledge, LAT1 expression in HNSCC has not been determined. Therefore, the present study aimed to examine the role of LAT1 expression in HNSCC. A total of three HNSCC cell lines (Sa3, HSC2 and HSC4) were used to investigate the characteristics of LAT1-positive cells, including their ability to form spheroids, and their invasion and migration. The present study also examined LAT1 by immunostaining of biopsy specimens from 174 patients diagnosed, treated and followed-up at Akita University (Akita, Japan) between January 2010 and December 2019, and overall survival, progression-free survival and multivariate analyses were performed. The results demonstrated that LAT1-positive cells in HNSCC were an independent prognostic factor for overall survival and progression-free survival, and were resistant to chemoradiation. Therefore, JPH203, a LAT1 inhibitor, may be effective in treating chemoradiotherapy-resistant HNSCC and may improve the prognosis of patients with HNSCC.

A curcumin analogue GO-Y030 depletes cancer stem cells by inhibiting the interaction between the HSP70/HSP40 complex and its substrates.

Cancer stem cells (CSCs) are proposed to be involved in tumor initiation and play important roles in cancer relapse, metastasis, and drug resistance. Therefore, the targeting of CSCs has potential for effective anticancer therapies. Curcumin is one of the most widely characterized phytochemicals with tumor-suppressive potential. GO-Y030 is a novel curcumin analogue exhibiting a much stronger growth-inhibitory effect than curcumin. In the present study, we verified the potency of GO-Y030 against a CSC population. We observed that GO-Y030 suppressed CSC sphere-forming ability in several cancer cell lines. Interestingly, a specific inhibitor of heat shock protein (HSP) 70 also exhibited effects similar to GO-Y030 (i.e. inhibition of CSC sphere formation and upregulation of HSP70 and HSP40 protein expression), suggesting that HSP70 and/or HSP40 might be target molecules of GO-Y030. We then performed an in vitro HSP70/HSP40-mediated refolding activity assay and observed that chaperone activity was efficiently inhibited by GO-Y030. Finally, we performed a substrate-binding assay to show that GO-Y030 reduced the binding of both HSP70 and HSP40 with their substrates. HSPs prevent denaturation or unfolding of client proteins under stressful conditions such as high temperature. Because CSCs by nature adapt to various stresses by reinforcing protein-folding activity, the function of HSP70/HSP40 is important for the maintenance of CSC population. Our data suggest that GO-Y030 may impair stress tolerance in CSCs by inhibiting the interaction of HSP70/HSP40 with their substrate proteins and disrupting the function of HSP70/HSP40, thereby contributing to a reduction of the CSC population.

GPNMB-Positive Cells in Head and Neck Squamous Cell Carcinoma-Their Roles in Cancer Stemness, Therapy Resistance, and Metastasis.

Objective: Despite the use of surgical and chemoradiation therapies, head and neck squamous cell carcinoma (HNSCC) still has a poor prognosis. Immune checkpoint inhibitors have been shown to prolong life expectancy but have limited efficacy. Glycoprotein nonmetastatic melanoma protein B (GPNMB) has received significant attention in breast cancer treatment, in which it has been associated with cancer stem cells (CSCs) and epithelial-mesenchymal transition (EMT); however, the function of GPNMB in HNSCC is completely unknown. This study aimed to clarify the characteristics of GPNMB-positive cells in vitro and their association with the prognosis by immunostaining clinical specimens. Methods: We examined the sphere formation, invasion, and migration ability of GPNMB-positive cells in four HNSCC cell lines in vitro. We also immunostained biopsy specimens with GPNMB from 174 patients with HNSCC diagnosed, treated, and followed-up in our institution to evaluate overall survival and progression-free survival. Results: GPNMB-positive cells showed enhanced sphere formation, invasion, and migration, suggesting that they could have CSC characteristics and the ability to induce EMT, as reported for breast cancer. Clinical specimens showed that overall survival was 39.4% and 57.8% (p = 0.045) and that progression-free survival was 27.6% and 51.6% (p = 0.013) for the high-expression and the low-expression groups, respectively, indicating poor prognosis for the high GPNMB group. The high GPNMB group was also more resistant to chemoradiation and bioradiotherapy. GPNMB was more highly expressed in metastatic lymph nodes than in the primary tumor. Conclusion: GPNMB-positive cells might have CSC characteristics and induce EMT. Detailed functional analyses of GPNMB in HNSCC and the establishment of therapies targeting GPNMB will lead to improved prognoses.

Tumor Infiltrating Lymphocytes are Prognostic Factors and Can Be Markers of Sensitivity to Chemoradiotherapy in Head and Neck Squamous Cell Carcinoma.

BACKGROUND: Tumor-infiltrating lymphocytes (TILs) are assessed by the ratio of the area of lymphocytes infiltrating the stroma. TILs are important in breast cancer and malignant melanoma and are being established as a marker of prognosis and sensitivity to chemotherapy. This has resulted in various therapies being developed in fields such as breast cancer. However, the evaluation of TILs in head and neck squamous cell carcinoma (HNSCC) is not progressing, and the prognosis is still poor. Thus, investigating whether or not the evaluation of TILs is also effective in HNSCC and prognoses can be predicted with just biopsy samples alone is required. METHODS: This study included 153 patients who were diagnosed with HNSCC between January 2010 and December 2019, underwent treatment, and could be followed up thereafter at our institution. RESULTS: TILs, overall survival (OS), and progression-free survival (PFS) were evaluated in all patients, the chemoradiotherapy arm, and the surgery arm. The cut-off value for TILs was 50%. In all patients, OS was 69.8% and 40.2% (P = 0.01) and PFS was 58.4% and 31.6% (P = 0.003) in the high and low TIL groups, respectively. Multivariate analyses revealed that TILs independently predicted prognosis. In the chemoradiotherapy arm, OS was 70.8% and 31.6% (P = 0.012) and PFS was 63.4% and 20.3% (P = 0.001) in the high and low TIL groups, respectively. No significant differences were noted in the surgery arm. CONCLUSIONS: In HNSCC, TILs can be used as a prognosis predictor and chemoradiotherapy biomarker. Assessments can be performed just with hematoxylin-eosin staining and is very simple. This will greatly contribute to report personalized therapy progress. Further evaluations and, thus, prospective clinical multicenter trials are needed to use TILs in clinical practice for HNSCC.

The investigation of salvage endoscopic laryngopharyngeal surgery after chemoradiotherapy.

INTRODUCTION: Endoscopic laryngopharyngeal surgery (ELPS) is an effective treatment for early-stage oropharyngeal and hypopharyngeal cancers. Since 2007, we have performed ELPS on 14 patients with early-stage cancer who had undergone radiation therapy (salvage ELPS). We discuss the beneficial effects and issues with salvage ELPS compared with those of fresh patients since we experienced some severe complications, such as ruptured pseudoaneurysm with salvage ELPS. AIM: To our knowledge, the efficacy and safety of ELPS following radiation therapy have not yet been evaluated, and several unknown factors exist. An evaluation was performed for assessing whether ELPS following radiation therapy is safe, similar to findings in fresh cases previously reported by us, and whether this treatment method can be efficacious. MATERIAL AND METHODS: We studied the cases of 14 patients who had undergone salvage ELPS after radiation therapy for head and neck cancer at Akita University Hospital between 2007 and 2018. RESULTS: The rate of recurrence of head and neck cancer at different sites after salvage ELPS was 48.9% at 2 years. Furthermore, deformation of the pharyngolarynx made it extremely difficult to perform surgery. We also experienced extremely severe complications of ruptured pseudoaneurysms. CONCLUSIONS: If salvage ELPS is performed after radiation therapy, patients should be followed up on an outpatient basis to monitor the onset of subsequent cancers. Complications may become severe; therefore, postoperative management should be performed cautiously. In particular, vulnerable sites, such as the piriform sinus, may not be indicated for surgery. At this stage, the expectation is that patients need to be methodically selected.

Two autopsy cases of desmoplastic small round cell tumor.

Desmoplastic small round cell tumor (DSRCT) is a rare aggressive malignant tumor. It is a refractory tumor and the median overall survival is very short. We report two autopsy cases of DSRCT, both of which were already advanced and metastasized at the first medical examination. Both cases showed typical DSRCT findings in terms of localization of the lesions, histopathology and genetics, but the rate of disease progression was quite different. Survival after initial symptoms in Case 1 was only 12 months. On the other hand, survival after primary hospitalization in Case 2 was 42 months. The Case 2 patient initially received chemotherapy for advanced pancreatic carcinoma, because a nodule of the pancreatic tail was found on computed tomography (CT) scan. After chemotherapy, tumor regression was observed on CT scan. It is thus implied that adoption of the regimen for pancreatic carcinoma might have been one of reasons of the long survival in Case 2.

An autopsy case of anaplastic lymphoma kinase-positive lung cancer exacerbated in a short period of time: a case report.

BACKGROUND: Anaplastic lymphoma kinase-positive lung cancer is a form of lung cancer that accounts for approximately 5% of non-small cell lung cancers. Recently, anaplastic lymphoma kinase inhibitors have been used for treatment of anaplastic lymphoma kinase-positive lung cancer, and their high clinical effect has also been demonstrated in cases of advanced stage lung cancer. Alectinib is an anaplastic lymphoma kinase inhibitor that it is recognized as a standard drug for primary therapy because of its superiority to crizotinib. CASE PRESENTATION: A 37-year-old Japanese man was admitted to our hospital due to multiple brain metastases. An autopsy report revealed that the cause of death was anaplastic lymphoma kinase-positive lung cancer, exacerbated in a short period despite treatment with alectinib. Necropsy revealed anaplastic lymphoma kinase-positive adenosquamous carcinoma of the lung, suggesting that it was involved in the prognosis of this patient. Based on the autopsy results, we reviewed the pathological tissue from transbronchial lung biopsy at the time of clinical diagnosis. The tissue specimen for clinical diagnosis in this case was a papillary adenocarcinoma. However, when this tissue was immunostained, thyroid transcription factor 1-negative and cytokeratin 5/6-positive parts were recognized. This result indicates that we could diagnose this patient as having had adenosquamous carcinoma of the lung. CONCLUSION: In cases of anaplastic lymphoma kinase-positive lung cancer poorly responsive to anaplastic lymphoma kinase inhibitors, re-examination of the tissue should be considered because there is a possibility of anaplastic lymphoma kinase-positive adenosquamous carcinoma.

An investigation on endoscopic laryngopharyngeal surgery and related outcomes.

INTRODUCTION: Robotic surgery is used in Europe and the US for oropharyngeal/hypopharyngeal cancers. Although robots can successfully perform procedures that are too delicate for surgeons and quickly learn accurate techniques, robotic surgery is not still authorized for the craniocervical region in Japan. In Japan, endoscopic laryngopharyngeal surgery (ELPS) is widely performed. Because oropharyngeal/hypopharyngeal cancer can be resected at an early stage, we have contributed to an improvement in the survival rate. AIM: To analyze clinical outcomes and risk factors of postoperative cervical lymph node metastases after ELPS. MATERIAL AND METHODS: Fifty-two patients with 71 superficial oropharyngeal/hypopharyngeal cancers were included. A Sato-type arcuation laryngoscope was inserted, and oropharyngeal and hypopharyngeal fields were secured. We have recently been performing head and neck surgery using only a flexible endoscope because gastroscopy and arcuation-type forceps interfere with each other. RESULTS: The 5-year survival rate was 95.2%. The risk factors of lymph node metastases were examined. The depth of the tumor significantly affected lymph node metastases. CONCLUSIONS: With a favorable 5-year survival rate and low functional impairment, ELPS is an extremely effective form of treatment. It can provide a clear field of view in the hypopharynx and has a low cost; hence, it should be further developed as a treatment method.

Intrinsic Oncogenic Function of Intracellular Connexin26 Protein in Head and Neck Squamous Cell Carcinoma Cells.

It has long been known that the gap junction is down-regulated in many tumours. One of the downregulation mechanisms is the translocation of connexin, a gap junction protein, from cell membrane into cytoplasm, nucleus, or Golgi apparatus. Interestingly, as tumours progress and reinforce their malignant phenotype, the amount of aberrantly-localised connexin increases in different malignant tumours including oesophageal squamous cell carcinoma, thus suggesting that such an aberrantly-localised connexin should be oncogenic, although gap junctional connexins are often tumour-suppressive. To define the dual roles of connexin in head and neck squamous cell carcinoma (HNSCC), we introduced the wild-type connexin26 (wtCx26) or the mutant Cx26 (icCx26) gene, the product of which carries the amino acid sequence AKKFF, an endoplasmic reticulum-Golgi retention signal, at the C-terminus and is not sorted to cell membrane, into the human FaDu hypopharyngeal cancer cell line that had severely impaired the expression of connexin during carcinogenesis. wtCx26 protein was trafficked to the cell membrane and formed gap junction, which successfully exerted cell-cell communication. On the other hand, the icCx26 protein was co-localised with a Golgi marker, as revealed by immunofluorescence, and thus was retained on the way to the cell membrane. While the forced expression of wtCx26 suppressed both cell proliferation in vitro and tumorigenicity in mice in vivo, icCx26 significantly enhanced both cell proliferation and tumorigenicity compared with the mock control clones, indicating that an excessive accumulation of connexin protein in intracellular domains should be involved in cancer progression and that restoration of proper subcellular sorting of connexin might be a therapeutic strategy to control HNSCC.

Prognostic role of regenerating gene-I in patients with stage-IV head and neck squamous cell carcinoma.

BACKGROUND: Regenerating gene (REG) family is composed of antiapoptotic factors and growth factors that affect epithelial cells within the digestive system. Regenerating gene-I has been studied in different cancers. However, it has never been studied in head and neck cancer. We investigated the expression of REG-I in head and neck SCC and its relevance to patient survival rates. METHODS: Untreated biopsy specimens of 60 patients with stage IV head and neck SCC were collected, and the expression of REG-I was evaluated using immunohistochemistry. The association between REG-I expression and clinico-pathological features or survival status of the patients was assessed by Chi-square test, Fisher's exact test and Kaplan-Meier method. Cox proportional hazard model was used to identify the independent prognostic factors. RESULTS: Incidence of lymphatic permeation, vascular invasion and pathological lymph nodes was significantly higher in REG-I negative group (p = 0.008, 0.030 and 0.015, respectively). Overall and cancer-free survival rates were significantly higher in REG-I positive group (p = 0.000434 and 1.0847E-8, respectively). Univariate analysis showed that REG-I was an independent prognostic factor for predicting long-term overall survival (p = 0.002), and multivariate analysis showed that REG-I and lymphatic permeation were independent prognostic factors for predicting long-term disease-free survival (p = 0.001 and 0.022, respectively). CONCLUSION: Our results showed for the first time that, REG-I is expressed in head and neck SCC. REG-I expression is associated with a longer survival status. We conclude that, REG-I might be a prognostic marker in head and neck SSC and should be further investigated.

Tumor necrosis factor-α promotes bile ductular transdifferentiation of mature rat hepatocytes in vitro.

We previously showed that mature hepatocytes could transdifferentiate into bile ductular cells when placed in a collagen-rich microenvironment. To explore the mechanism of transdifferentiation, we examined whether inflammatory cytokines affected the phenotype of hepatocytes in a three-dimensional culture system. Spheroidal aggregates of rat hepatocytes were embedded within a type I collagen gel matrix and cultured in the presence of various cytokines. In the control, hepatocytes gradually lost expression of albumin, tyrosine aminotransferase, and hepatocyte nuclear factor (HNF)-4α, while aberrantly expressed bile ductular markers, including cytokeratin 19 (CK 19) and spermatogenic immunoglobulin superfamily (SgIGSF). Among the cytokines examined, tumor necrosis factor (TNF)-α inhibited expression of albumin and HNF-4α, both at mRNA and protein levels. After culturing for 2 weeks with TNF-α, hepatocytic spheroids were transformed into extensively branching tubular structures composed of CK 19- and SgIGSF-positive small cuboidal cells. These cells responded to secretin with an increase in secretion and expressed functional bile duct markers. TNF-α also induced the phosphorylation of Jun N-terminal kinase (JNK) and c-Jun, and the morphogenesis was inhibited by SP600125, a specific JNK inhibitor. Furthermore, in chronic rat liver injury induced by CCl(4) , ductular reaction in the centrilobular area demonstrated strong nuclear staining of phosphorylated c-Jun. Our results demonstrate that TNF-α promotes the ductular transdifferentiation of hepatocytes and suggest a role of TNF-α in the pathogenesis of ductular reaction.

Recovery of mature hepatocytic phenotype following bile ductular transdifferentiation of rat hepatocytes in vitro.

We previously demonstrated that mature rat hepatocytes transdifferentiate to bile ductular cells when cultured in a three-dimensional collagen-rich matrix. Here, we show that the phenotype of transdifferentiated hepatocytes can be reversed by modulating culture conditions. Spheroidal aggregates of hepatocytes were cultured within a collagen gel matrix in the presence of serum and tumor necrosis factor-α. Spheroids transformed into ductular structures composed of small cuboidal cells, lost the expression of hepatocytic markers, whereas aberrantly expressed bile ductular markers. The transdifferentiated cells were then retrieved from the gels, plated on surfaces coated with a basement membrane-like material, and cultured in serum-free media. Cells spontaneously formed spheroidal aggregates and recovered hepatocytic phenotype. Dexamethasone (Dex), which suppressed the phosphorylation of ERK and Jun N-terminal kinase, facilitated the recovery, and the combination with interleukin-6 or oncostatin M resulted in the recovery of hepatocyte nuclear factor 4 α protein expression and the typical hepatocytic morphology, and a decrease in the expression of bile ductular markers. A cDNA microarray analysis revealed that the hepatocyte-specific mRNA expression profile was recovered in these cells. Our results demonstrate that hepatocytes are able to recover their phenotypes following bile ductular transdifferentiation, suggesting that hepatocytic and bile ductular phenotypes may be mutually reversible.

Smad ubiquitination regulatory factor-2 controls gap junction intercellular communication by modulating endocytosis and degradation of connexin43.

Gap junctions consist of arrays of intercellular channels that enable adjacent cells to communicate both electrically and metabolically. Gap junction channels are made of a family of integral membrane proteins called connexins, of which the best-studied member is connexin43. Gap junctions are dynamic plasma membrane domains, and connexin43 has a high turnover rate in most tissue types. However, the mechanisms involved in the regulation of connexin43 endocytosis and transport to lysosomes are still poorly understood. Here, we demonstrate by live-cell imaging analysis that treatment of cells with 12-O-tetradecanoylphorbol 13-acetate (TPA) induces endocytosis of subdomains of connexin43 gap junctions. The internalized, connexin43-enriched vesicles were found to fuse with early endosomes, which was followed by transport of connexin43 to the lumen of early endosomes. The HECT E3 ubiquitin ligase smad ubiquitination regulatory factor-2 (Smurf2) was found to be recruited to connexin43 gap junctions in response to TPA treatment. Depletion of Smurf2 by small interfering RNA resulted in enhanced levels of connexin43 gap junctions between adjacent cells and increased gap junction intercellular communication. Smurf2 depletion also counteracted the TPA-induced endocytosis and degradation of connexin43. Collectively, these data identify Smurf2 as a novel regulator of connexin43 gap junctions.

Cytoplasmic accumulation of connexin32 expands cancer stem cell population in human HuH7 hepatoma cells by enhancing its self-renewal.

Although the connexin32 (Cx32)-mediated gap junction is abolished in hepatocellular carcinoma (HCC), the expression of cytoplasmic Cx32 tends to increase in correspondence with the grade of malignancy. Establishing a Tet-off expression system in human nonmetastatic HuH7 HCC cells where cytoplasmic Cx32 was overexpressed by doxycycline (Dox) withdrawal, we previously demonstrated that overexpression of cytoplasmic Cx32 made HuH7 cells metastatic in mice. In our study, hypothesizing that the cytoplasmic Cx32-induced metastasis may involve expansion of the cancer stem cell (CSC) population, we examined whether cytoplasmic Cx32 controlled the size of the side population (SP) in HuH7 Tet-off Cx32 cells. Fluorescence-activated cell sorting revealed that SP was expanded in a Dox-free medium compared with a Dox-supplemented one. Although cytoplasmic Cx32 did not block maturation from SP to non-SP, purified SP reconstituted a larger SP fraction in the Dox-free medium than in the Dox-supplemented one. Furthermore, although SP from HuH7 Tet-off mock cells formed a similar number of CSC spheres of a similar size whether with or without Dox, SP from HuH7 Tet-off Cx32 cells developed a greater number of larger CSC spheres in the Dox-free medium than in the Dox-supplemented one. Taken together, these results suggest that accumulation of cytoplasmic Cx32 should enhance self-renewal of CSC to expand the CSC population in HCC.

Significance of integrin αvß5 and erbB3 in enhanced cell migration and liver metastasis of colon carcinomas stimulated by hepatocyte-derived heregulin.

To study the mechanisms of the highly liver-metastatic character of colon carcinoma cells, we studied the expression pattern of surface integrins on LS-LM6 (a highly liver-metastatic human colon cancer cell line) and the effects of hepatocyte-derived soluble factors on cell migration. LS-LM6 showed significantly higher expression of integrin αvß5, a ligand for vitronectin (VN), as compared with its parental cell line (LS174T). A conditioned medium of cultured mouse hepatocytes enhanced VN-mediated cell migration of LS-LM6, which was blocked by neutralizing antibody against integrin αvß5, while the medium did not affect cell adhesion to VN-coated plastic surfaces. The conditioned medium induced phosphorylation of erbB3 and its heterodimeric partner, erbB2. Heregulin (HRG), a ligand for erbB3, exerted similar effects on VN-mediated cell migration and phosphorylation of erbB3 and erbB2. The conditioned medium contained HRG, and depletion of HRG from the medium by pre-absorption with HRG antibody abolished its effects on cell migration. Heregulin (HRG) was expressed in some hepatocytes in the liver with carcinoma cell metastasis. Furthermore, knockdown of integrin αv and erbB3 by small-interfering RNAs significantly inhibited cell migration induced by HRG as well as liver metastasis in vivo. Finally, we found that HRG-induced cell migration was associated with marked phosphorylation of Akt and that cell migration was suppressed by treatment with specific inhibitors of phosphatidylinositol 3-kinase. Our study suggests that hepatocyte-derived HRG might participate in a highly liver-metastatic phenotype of LS-LM6 through enhancement of integrin αvß5-mediated cell migration and erbB3/erbB2 signaling.