Live-cell imaging and CLEM reveal the existence of ACTN4-dependent ruffle-edge lamellipodia acting as a novel mode of cell migration.

α-Actinin-4 (ACTN4) expression levels are correlated with the invasive and metastatic potential of cancer cells; however, the underlying mechanism remains unclear. Here, we identified ACTN4-localized ruffle-edge lamellipodia using live-cell imaging and correlative light and electron microscopy (CLEM). BSC-1 cells expressing EGFP-ACTN4 showed that ACTN4 was most abundant in the leading edges of lamellipodia, although it was also present in stress fibers and focal adhesions. ACTN4 localization in lamellipodia was markedly diminished by phosphoinositide 3-kinase inhibition, whereas its localization in stress fibers and focal adhesions remained. Furthermore, overexpression of ACTN4, but not ACTN1, promoted lamellipodial formation. Live-cell analysis demonstrated that ACTN4-enriched lamellipodia are highly dynamic and associated with cell migration. CLEM revealed that ACTN4-enriched lamellipodia exhibit a characteristic morphology of multilayered ruffle-edges that differs from canonical flat lamellipodia. Similar ruffle-edge lamellipodia were observed in A549 and MDA-MB-231 invasive cancer cells. ACTN4 knockdown suppressed the formation of ruffle-edge lamellipodia and cell migration during wound healing in A549 monolayer cultures. Additionally, membrane-type 1 matrix metalloproteinase was observed in the membrane ruffles, suggesting that ruffle-edge lamellipodia have the ability to degrade the extracellular matrix and may contribute to active cell migration/invasion in certain cancer cell types.

Identification of TPI1 As a potential therapeutic target in pancreatic cancer with dependency of TP53 mutation using multi-omics analysis.

Mutations of KRAS, CDKN2A, TP53, and SMAD4 are the four major driver genes for pancreatic ductal adenocarcinoma (PDAC), of which mutations of KRAS and TP53 are the most frequently recognized. However, molecular-targeted therapies for mutations of KRAS and TP53 have not yet been developed. To identify novel molecular targets, we newly established organoids with the Kras mutation (KrasmuOR) and Trp53 loss of function using Cre transduction and CRISPR/Cas9 (Krasmu/p53muOR) from murine epithelia of the pancreatic duct in KrasLSL-G12D mice, and then analyzed the proteomic and metabolomic profiles in both organoids by mass spectrometry. Hyperfunction of the glycolysis pathway was recognized in Krasmu/p53muOR compared with KrasmuOR. Loss of function of triosephosphate isomerase (TPI1), which is involved in glycolysis, induced a reduction of cell proliferation in human PDAC cell lines with the TP53 mutation, but not in PDAC or in human fibroblasts without TP53 mutation. The TP53 mutation is clinically recognized in 70% of patients with PDAC. In the present study, protein expression of TPI1 and nuclear accumulation of p53 were recognized in the same patients with PDAC. TPI1 is a potential candidate therapeutic target for PDAC with the TP53 mutation.

Phosphoproteomic Analysis Identified Mutual Phosphorylation of FAK and Src as a Mechanism of Osimertinib Resistance in EGFR-Mutant Lung Cancer.

Introduction: Osimertinib is a standard treatment for patients with EGFR-mutant NSCLC. Although some osimertinib resistance mechanisms have been identified, nearly 50% of the mechanisms remain to be elucidated. This study was aimed at identifying non-genetic mechanisms underlying osimertinib resistance. Methods: We established two osimertinib-resistant cell lines from EGFR mutation-positive PC-9 and HCC827 NSCLC cell lines (PC-9OR and HCC827OR, respectively) using a stepwise method. We compared the phosphoproteomic profiles of the osimertinib-resistant and parental cells using mass spectrometry. Upstream kinases were identified using the application Kinase Enrichment Analysis version 3. Results: Phosphoproteomic analysis revealed 80 phosphorylation sites that were mutually up-regulated in PC-9OR and HCC827OR cells. The Kinase Enrichment Analysis version 3 analysis identified focal adhesion kinase (FAK) and proto-oncogene tyrosine-protein kinase Src (Src) as upstream kinases of these up-regulated phosphoproteins. The small-interfering RNA-mediated knockdown of FAK reduced Src phosphorylation and that of Src reduced FAK phosphorylation in both cell lines. Furthermore, FAK- or Src-specific small-interfering RNA treatments restored EGFR phosphorylation in PC-9OR and HCC827OR cells. The combination of FAK and Src inhibitors inhibited PC-9OR and HCC827OR cell proliferation in vitro and suppressed tumor growth in a xenograft mouse model. Immunohistochemistry of tumors from patients with EGFR-mutant NSCLC suggested that phosphorylated FAK and Src are involved in initial and acquired resistance to osimertinib. Conclusions: Phosphoproteomic analysis may help elucidate the mechanisms of resistance to molecular-targeted therapies in lung cancer. Mutual phosphorylation of FAK and Src is involved in osimertinib resistance. Thus, FAK and Src inhibition may be novel treatment strategies for osimertinib-resistant NSCLC.

Clinical development of a blood biomarker using apolipoprotein-A2 isoforms for early detection of pancreatic cancer.

BACKGROUND: We have previously reported apolipoprotein A2-isoforms (apoA2-is) as candidate plasma biomarkers for early-stage pancreatic cancer. The aim of this study was the clinical development of apoA2-is. METHODS: We established a new enzyme-linked immunosorbent sandwich assay for apoA2-is under the Japanese medical device Quality Management System requirements and performed in vitro diagnostic tests with prespecified end points using 2732 plasma samples. The clinical equivalence and significance of apoA2-is were compared with CA19-9. RESULTS: The point estimate of the area under the curve to distinguish between pancreatic cancer (n = 106) and healthy controls (n = 106) was higher for apoA2-ATQ/AT [0.879, 95% confidence interval (CI): 0.832-0.925] than for CA19-9 (0.849, 95% CI 0.793-0.905) and achieved the primary end point. The cutoff apoA2-ATQ/AT of 59.5 µg/mL was defined based on a specificity of 95% in 2000 healthy samples, and the reliability of specificities was confirmed in two independent healthy cohorts as 95.3% (n = 106, 95% CI 89.4-98.0%) and 95.8% (n = 400, 95% CI 93.3-97.3%). The sensitivities of apoA2-ATQ/AT for detecting both stage I (47.4%) and I/II (50%) pancreatic cancers were higher than those of CA19-9 (36.8% and 46.7%, respectively). The combination of apoA2-ATQ/AT (cutoff, 59.5 µg/mL) and CA19-9 (37 U/mL) increased the sensitivity for pancreatic cancer to 87.7% compared with 69.8% for CA19-9 alone. The clinical performance of apoA2-is was blindly confirmed by the National Cancer Institute Early Detection Research Network. CONCLUSIONS: The clinical performance of ApoA2-ATQ/AT as a blood biomarker is equivalent to or better than that of CA19-9.

Identification of activity-based biomarkers for early-stage pancreatic tumors in blood using single-molecule enzyme activity screening.

Single-molecule enzyme activity-based enzyme profiling (SEAP) is a methodology to globally analyze protein functions in living samples at the single-molecule level. It has been previously applied to detect functional alterations in phosphatases and glycosidases. Here, we expand the potential for activity-based biomarker discovery by developing a semi-automated synthesis platform for fluorogenic probes that can detect various peptidases and protease activities at the single-molecule level. The peptidase/protease probes were prepared on the basis of a 7-amino-4-methylcoumarin fluorophore. The introduction of a phosphonic acid to the core scaffold made the probe suitable for use in a microdevice-based assay, while phosphonic acid served as the handle for the affinity separation of the probe using Phos-tag. Using this semi-automated scheme, 48 fluorogenic probes for the single-molecule peptidase/protease activity analysis were prepared. Activity-based screening using blood samples revealed altered single-molecule activity profiles of CD13 and DPP4 in blood samples of patients with early-stage pancreatic tumors. The study shows the power of single-molecule enzyme activity screening to discover biomarkers on the basis of the functional alterations of proteins.

Thioester-Based Coupled Fluorogenic Assays in Microdevice for the Detection of Single-Molecule Enzyme Activities of Esterases with Specified Substrate Recognition.

Single-molecule enzyme activity assay is a platform that enables the analysis of enzyme activities at single proteoform level. The limitation of the targetable enzymes is the major drawback of the assay, but the general assay platform is reported to study single-molecule enzyme activities of esterases based on the coupled assay using thioesters as substrate analogues. The coupled assay is realized by developing highly water-soluble thiol-reacting probes based on phosphonate-substituted boron dipyrromethene (BODIPY). The system enables the detection of cholinesterase activities in blood samples at single-molecule level, and it is shown that the dissecting alterations of single-molecule esterase activities can serve as an informative platform for activity-based diagnosis.

Apolipoprotein A2 isoforms associated with exocrine pancreatic insufficiency in early chronic pancreatitis.

BACKGROUND AND AIM: Apolipoprotein A2 (apoA2) isoforms have been reported to undergo the aberrant processing in pancreatic cancer and pancreatic risk populations compared with that in healthy subjects. This study aimed to clarify whether apoA2 isoforms were as useful as N-benzoyl-p-aminobenzoic acid (BT-PABA) test for exocrine pancreatic dysfunction markers in patients with early chronic pancreatitis (ECP). METHODS: Fifty consecutive patients with functional dyspepsia with pancreatic enzyme abnormalities (FD-P) (n = 18), with ECP (n = 20), and asymptomatic patients with pancreatic enzyme abnormalities (AP-P) (n = 12) based on the Rome IV classification and the Japan Pancreatic Association were enrolled in this study. The enrolled patients were evaluated using endoscopic ultrasonography and endoscopic ultrasonography elastography. Five pancreatic enzymes were estimated. Pancreatic exocrine function was analyzed using the BT-PABA test. Lighter and heavier apoA2 isoforms, AT and ATQ levels were measured by enzyme-linked immunosorbent assay methods. RESULTS: There were no significant differences in clinical characteristics such as age, gender, body mass index, alcohol consumption and smoking among patients with AP-P, FD-P, and ECP. The BT-PABA test and lighter apoA2 isoform, AT level in the enrolled patients had a significant correlation (P < 0.01). The BT-PABA test in patients with ECP was significantly lower (P = 0.04) than that in AP-P. ApoA2-AT level in patients with ECP was lower than that in AP-P, albeit, insignificantly. Interestingly, apo A2-AT level was significantly (P = 0.041) associated with exocrine pancreatic insufficiency by multiple logistic regression analysis. CONCLUSIONS: ApoA2-AT level is a useful tool to evaluate exocrine pancreatic insufficiency in the early stage of chronic pancreatitis.

Development of fluorogenic substrates for colorectal tumor-related neuropeptidases for activity-based diagnosis.

The M3 metalloproteases, neurolysin and THOP1, are neuropeptidases that are expressed in various tissues and metabolize neuropeptides, such as neurotensin. The biological roles of these enzymes are not well characterized, partially because the chemical tools to analyse their activities are not well developed. Here, we developed a fluorogenic substrate probe for neurolysin and thimet oligopeptidase 1 (THOP1), which enabled the analysis of enzymatic activity changes in tissue and plasma samples. In particular, the probe was useful for studying enzyme activities in a single-molecule enzyme assay platform, which can detect enzyme activity with high sensitivity. We detected the activity of neurolysin in plasma samples and revealed higher enzyme activity in the blood samples of patients with colorectal tumor. The result indicated that single-molecule neurolysin activity is a promising candidate for a blood biomarker for colorectal cancer diagnosis.

Copy number gain of ACTN4 is associated with poor prognosis in patients with upper urinary tract urothelial carcinoma.

α-Actinin4 (ACTN4), an isoform of non-muscular α-actinin, is involved in enhancing cell motility and promoting cancer infiltration and metastasis in various cancers. However, information remains limited regarding the pathological significance of ACTN4 expression in upper urinary tract urothelial carcinomas (UUTUCs). We obtained tumor samples from 168 consecutive patients with newly diagnosed UUTUCs (92 with renal pelvic cancers and 76 with ureteral cancers), who were treated with nephroureterectomy or partial ureterectomy, and analyzed the expression of the ACTN4 protein and the amplification of ACTN4 using immunohistochemistry and fluorescence in situ hybridization (FISH), respectively. The median follow-up duration was 65 months. Among 168 cases, 49 (29%) showed ACTN4 protein overexpression and 25 (15%) showed copy number gain (≥4 copies per cell) of ACTN4. The copy number gain of ACTN4 detected using FISH significantly correlated with ACTN4 protein overexpression and several adverse clinicopathological factors, including higher pathological T stage, lymphovascular invasion, lymph node metastasis, positive surgical margin, concomitant subtype histology, and non-papillary gross finding. Cox univariate regression analyses revealed that both copy number gain of ACTN4 and ACTN4 protein overexpression were significant risk factors for extraurothelial recurrence and death (each p < 0.0001), but multivariate analysis revealed that only copy number gain of ACTN4 was an independent risk factor for extraurothelial recurrence and death (p = 0.038 and 0.027, hazard ratio = 2.16 and 2.17, respectively). This is the first study demonstrating the aberrant expression status of ACTN4 in UUTUC and indicating its putative usefulness as a prognostic indicator in patients with UUTUC.

Integration of pharmacoproteomic and computational approaches reveals the cellular signal transduction pathways affected by apatinib in gastric cancer cell lines.

Apatinib is known to be a highly selective vascular endothelial growth factor receptor 2 (VEGFR2) inhibitor with anti-angiogenic and anti-tumor properties. In a phase III study, the objective response rate to apatinib was low. It remains unclear why the effectivity of apatinib varies among patients and what type of patients are candidates for the treatment. In this study, we investigated the anti-tumor efficacy of apatinib against 13 gastric cancer cell lines and found that it differed depending on the cell line. Using integrated wet and dry approaches, we showed that apatinib was a multi-kinase inhibitor of c-Kit, RAF1, VEGFR1, VEGFR2, and VEGFR3, predominantly inhibiting c-Kit. Notably, KATO-III, which was the most apatinib-sensitive among the gastric cancer cell lines investigated, was the only cell line expressing c-Kit, RAF1, VEGFR1, and VEGFR3 but not VEGFR2. Furthermore, we identified SNW1 as a molecule affected by apatinib that plays an important role in cell survival. Finally, we identified the molecular network related to SNW1 that was affected by treatment with apatinib. These results suggest that the mechanism of action of apatinib in KATO-III cells is independent of VEGFR2 and that the differential efficacy of apatinib was due to differences in expression patterns of receptor tyrosine kinases. Furthermore, our results suggest that the differential efficacy of apatinib in gastric cell lines may be attributed to SNW1 phosphorylation levels at a steady state. These findings contribute to a deeper understanding of the mechanism of action of apatinib in gastric cancer cells.

Liquid Biopsy for Oral Cancer Diagnosis: Recent Advances and Challenges.

"Liquid biopsy" is an efficient diagnostic tool used to analyse biomaterials in human body fluids, such as blood, saliva, breast milk, and urine. Various biomaterials derived from a tumour and its microenvironment are released into such body fluids and contain important information for cancer diagnosis. Biomaterial detection can provide "real-time" information about individual tumours, is non-invasive, and is more repeatable than conventional histological analysis. Therefore, over the past two decades, liquid biopsy has been considered an attractive diagnostic tool for malignant tumours. Although biomarkers for oral cancer have not yet been adopted in clinical practice, many molecular candidates have been investigated for liquid biopsies in oral cancer diagnosis, such as the proteome, metabolome, microRNAome, extracellular vesicles, cell-free DNAs, and circulating tumour cells. This review will present recent advances and challenges in liquid biopsy for oral cancer diagnosis.

Benefits from Adjuvant Chemotherapy in Patients with Resected Non-Small Cell Lung Cancer: Possibility of Stratification by Gene Amplification of ACTN4 According to Evaluation of Metastatic Ability.

Surgical treatment is the best curative treatment option for patients with non-small cell lung cancer (NSCLC), but some patients have recurrence beyond the surgical margin even after receiving curative surgery. Therefore, therapies with anti-cancer agents also play an important role perioperatively. In this paper, we review the current status of adjuvant chemotherapy in NSCLC and describe promising perioperative therapies, including molecularly targeted therapies and immune checkpoint inhibitors. Previously reported biomarkers of adjuvant chemotherapy for NSCLC are discussed along with their limitations. Adjuvant chemotherapy after resective surgery was most effective in patients with metastatic lesions located just outside the surgical margin; in addition, these metastatic lesions were the most sensitive to adjuvant chemotherapy. Thus, the first step in predicting patients who have sensitivity to adjuvant therapies is to perform a qualified evaluation of metastatic ability using markers such as actinin-4 (ACTN4). In this review, we discuss the potential use of biomarkers in patient stratification for effective adjuvant chemotherapy and, in particular, the use of ACTN4 as a possible biomarker for NSCLC.

Risk stratification of pancreatic cancer by a blood test for apolipoprotein A2-isoforms.

Though pancreatic cancer is uncommon, with an age-adjusted annual incidence of 12.9 cases per 100,000 person-years, it is considered a refractory cancer due to the mortality of 11.0 per 100,000 person-years. To efficiently identify patients with potentially surgically-curable pancreatic cancer, high-risk individuals (HRIs) for pancreatic cancer should be identified by easily and minimally invasive methods from the general population. We have identified unique processing patterns in the C-terminal amino acids of apolipoprotein A2 homodimer in the blood of patients with pancreatic cancer and in HRIs, and we called them apoA2-isoforms (apoA2-i). We then established an enzyme-linked immunosorbent assay (ELISA) to measure circulating apoA2-i in the blood stream. The diagnostic accuracy of apoA2-i to distinguish pancreatic cancer HRIs was verified by several retrospective studies, blind testing with the National Cancer Institute (NCI) Early Detection Research Network (EDRN), a prospective study with prediagnostic samples organized by the European Prospective Investigation into Cancer and Nutrition (EPIC) study, and the prospective screening study of pancreatic cancer in Kobe.The apoA2-i blood test is a potential biomarker to identify HRIs and the curative stage of pancreatic cancer in the general population.

Temporal dynamics from phosphoproteomics using endoscopic biopsy specimens provides new therapeutic targets in stage IV gastric cancer.

Phosphoproteomic analysis expands our understanding of cancer biology. However, the feasibility of phosphoproteomic analysis using endoscopically collected tumor samples, especially with regards to dynamic changes upon drug treatment, remains unknown in stage IV gastric cancer. Here, we conducted a phosphoproteomic analysis using paired endoscopic biopsy specimens of pre- and post-treatment tumors (Ts) and non-tumor adjacent tissues (NATs) obtained from 4 HER2-positive gastric cancer patients who received trastuzumab-based treatment and from pre-treatment Ts and NATs of 4 HER2-negative gastric cancer patients. Our analysis identified 14,622 class 1 phosphosites with 12,749 quantified phosphosites and revealed molecular changes by HER2 positivity and treatment. An inhibitory signature of the ErbB signaling was observed in the post-treatment HER2-positive T group compared with the pre-treatment HER2-positive T group. Phosphoproteomic profiles obtained by a case-by-case review using paired pre- and post-treatment HER2-positive T could be utilized to discover predictive or resistant biomarkers. Furthermore, these data nominated therapeutic kinase targets which were exclusively activated in the patient unresponded to the treatment. The present study suggests that a phosphoproteomic analysis of endoscopic biopsy specimens provides information on dynamic molecular changes which can individually characterize biologic features upon drug treatment and identify therapeutic targets in stage IV gastric cancer.

Development of Biomarkers to Predict Recurrence by Determining the Metastatic Ability of Cancer Cells.

Adjuvant chemotherapy is administered to cancer patients after curative resection but is unnecessary when patients without micro-metastatic lesions undergo a perfectly curative surgical procedure. Patients who need adjuvant chemotherapy are those with micro-metastases outside the resection area that are not detectable by imaging, despite curative resection at primary sites. If biomarkers that reflect metastatic potential could be developed, personalized adjuvant chemotherapy could be provided in clinical settings. Actinin-4 (ACTN4, gene name ACTN4) is an actin-bundling protein identified in 1998 as a novel molecule involved in cancer invasion and metastasis. Overexpression of actinin-4 protein in cancer cells leads to an invasive phenotype, and patients with gene amplification of ACTN4 have a worse prognosis than patients with a normal copy number for cancers of the pancreas, lung, and salivary glands, among others. This review summarizes the biological roles of actinin-4 in cancer invasion and metastasis and examines the potential usefulness of actinin-4 as a biomarker for evaluation of metastatic ability.

RIOK2 Contributes to Cell Growth and Protein Synthesis in Human Oral Squamous Cell Carcinoma.

Ribosomes are responsible for the protein synthesis that maintains cellular homeostasis and is required for the rapid cellular division of cancer cells. However, the role of ribosome biogenesis mediators in the malignant behavior of tongue squamous cell carcinoma (TSCC) is unknown. In this study, we found that the expression of RIOK2, a key enzyme involved in the maturation steps of the pre-40S ribosomal complex, was significantly associated with poorer overall survival in patients with TSCC. Further, multivariate analysis revealed that RIOK2 is an independent prognostic factor (hazard ratio, 3.53; 95% confidence interval, 1.19-10.91). Inhibition of RIOK2 expression by siRNA decreased cell growth and S6 ribosomal protein expression in oral squamous cell carcinoma cell lines. RIOK2 knockdown also led to a significant decrease in the protein synthesis in cancer cells. RIOK2 has potential application as a novel therapeutic target for TSCC treatment.

Alpha-actinin-4 (ACTN4) gene amplification is a predictive biomarker for adjuvant chemotherapy with tegafur/uracil in stage I lung adenocarcinomas.

Although adjuvant tegafur/uracil (UFT) is recommended for patients with completely resected stage I non-small-cell lung cancer (NSCLC) in Japan, only one-third of cases has received adjuvant chemotherapy (ADJ) according to real-world data. Therefore, robust predictive biomarkers for selecting ADJ or observation (OBS) without ADJ are needed. Patients who underwent complete resection of stage I lung adenocarcinoma with or without adjuvant UFT were enrolled. The status of ACTN4 gene amplification was analyzed by FISH. Statistical analyses to determine whether the status of ACTN4 gene amplification affected recurrence-free survival (RFS) were carried out. Formalin-fixed, paraffin-embedded samples from 1136 lung adenocarcinomas were submitted for analysis of ACTN4 gene amplification. Ninety-nine (8.9%) of 1114 cases were positive for ACTN4 gene amplification. In the subgroup analysis of patients aged 65 years or older, the ADJ group had better RFS than the OBS group in the ACTN4-positive cohort (hazard ratio [HR], 0.084, 95% confidence interval [CI], 0.009-0.806; P = .032). The difference in RFS between the ADJ group and the OBS group was not significant in ACTN4-negative cases (all ages: HR, 1.214; 95% CI, 0.848-1.738; P = .289). Analyses of ACTN4 gene amplification contributed to the decision regarding postoperative ADJ for stage I lung adenocarcinomas, preventing recurrence, improving the quality of medical care, preventing the unnecessary side-effects of ADJ, and saving medical costs.

Noninvasive risk stratification of intraductal papillary mucinous neoplasia with malignant potential by serum apolipoprotein-A2-isoforms.

Intraductal papillary mucinous neoplasms (IPMNs) are premalignant lesions of pancreatic cancer. An accurate serum biomarker, which allows earlier identification of asymptomatic individuals with high-risk for developing cancer, is of urgent need. Apolipoprotein A2-isoforms (apoA2-i) have previously been identified as biomarkers in pancreatic cancer. This study investigates a potential clinical application of the serum apoA2-i for risk stratification of IPMN and associated cancer. The concentrations of apoA2-i were retrospectively determined in 523 patient sera specimen, composed of 305 IPMNs with preinvasive lesions with different grades of dysplasia and invasive cancer, 140 pancreatic ductal adenocarcinoma, 78 with other cystic lesions and healthy controls cohorts, using an apoA2-i enzyme-linked immunosorbent assay kit. The diagnostic performance of serum apoA2-i was assessed and compared to routine clinical marker CA 19-9. ApoA2-i levels were significantly reduced in all IPMN samples regardless of stage compared to healthy controls. Receiver operating characteristic curve analysis of IPMNs with high-grade dysplasia and IPMN with associated carcinoma revealed the area under curve (AUC) of 0.91 and >0.94, respectively. The respective sensitivities were 70% and 83% with a specificity of 95%, and significantly higher than the gold standard biomarker CA 19-9. AUC values of apoA2-i for detecting IPMN-associated carcinoma of colloid and ductal subtypes were 0.990 and 0.885, respectively. ApoA2-i has the potential to early detect the risk of malignancy of patients with IPMN. The serological apoA2-i test in combination with imaging modalities could help improve the diagnosis of IPMN malignancy. Further validation in larger and independent international cohort studies is needed.

Possible Therapeutic Strategy Involving the Purine Synthesis Pathway Regulated by ITK in Tongue Squamous Cell Carcinoma.

The epidermal growth factor receptor is the only available tyrosine kinase molecular target for treating oral cancer. To improve the prognosis of tongue squamous cell carcinoma (TSCC) patients, a novel molecular target for tyrosine kinases is thus needed. We examined the expression of interleukin-2-inducible T-cell kinase (ITK) using immunohistochemistry, and the biological function of ITK was investigated using biochemical, phosphoproteomic, and metabolomic analyses. We found that ITK is overexpressed in TSCC patients with poor outcomes. The proliferation of oral cancer cell lines expressing ITK via transfection exhibited significant increases in three-dimensional culture assays and murine inoculation models with athymic male nude mice as compared with mock control cells. Suppressing the kinase activity using chemical inhibitors significantly reduced the increase in cell growth induced by ITK expression. Phosphoproteomic analyses revealed that ITK expression triggered phosphorylation of a novel tyrosine residue in trifunctional purine biosynthetic protein adenosine-3, an enzyme in the purine biosynthesis pathway. A significant increase in de novo biosynthesis of purines was observed in cells expressing ITK, which was abolished by the ITK inhibitor. ITK thus represents a potentially useful target for treating TSCC through modulation of purine biosynthesis.