Punicalagin alleviates the hyperproliferation of keratinocytes in psoriasis through inhibiting SKP2 expression.

Psoriasis is a chronic inflammatory skin disorder characterized by abnormal keratinocytes proliferation and multiple immune cells infiltration in the dermis and epidermis. Although most psoriasis-related researches have been concentrated on the interleukin-23 (IL-23)/interleukin-17 (IL-17) axis, new data suggest that keratinocytes also play a pivotal role in psoriasis. Previously, we found that punicalagin (PUN), a bioactive ellagitannin extracted from Pericarpium Granati (the pericarpium of Punica granatum L.), exerts a therapeutic effect on psoriasis. However, the underlying mechanism, especially its potential modulatory effect on keratinocytes, remains obscure. Our study aims to reveal the potential regulatory effect and its underlying cellular mechanism of PUN on the hyperproliferation of keratinocytes. We used tumor necrosis factor α (TNF-α), IL-17A and interleukin-6 (IL-6) to induce abnormal proliferation of HaCaT cells (Human Keratinocytes Cells) in vitro. Then, we evaluated the effects of PUN through MTT assay, EdU staining and cell cycle detection. Finally, we explored the underlying cellular mechanisms of PUN via RNA-sequencing, WB in vitro and in vivo. Here, we found that PUN can directly and dose-dependently decrease TNF-α, IL-17A and IL-6-induced abnormal proliferation of HaCaT cells in vitro. Mechanically, PUN suppresses the hyperproliferation of keratinocytes through repressing S-phase kinase-associated protein 2 (SKP2) expression in vitro and in vivo. Moreover, overexpression of SKP2 can partly abolish PUN-mediated inhibition of aberrantly proliferative keratinocytes. These results illustrate that PUN can reduce the severity of psoriasis through directly repressing SKP2-mediated abnormal proliferation of keratinocytes, which gives new insight into the therapeutic mechanism of PUN on psoriasis. Moreover, these findings imply that PUN might be a promising drug candidate for the treatment of psoriasis.

Ethyl acetate extract of Antenoron Filiforme inhibits the proliferation of triple negative breast cancer cells via suppressing Skp2/p21 signaling axis.

BACKGROUND: Triple negative breast cancer (TNBC) has the worst prognosis of the any breast cancer subtype, and the efficient therapeutical treatment is extremely limited. Antenoron filiforme (Thunb.) Roberty & Vautier (AF) is a Traditional Chinese Medicine (TCM), which is well-known for a diverse array of pharmacological activities, including but not limited to anti-inflammatory, antioxidant and anti-tumors properties. Clinically, AF is commonly prescribed for the treatment of gynecological diseases. PURPOSE: Since TNBC is one of the worst gynecological diseases, the objective of this research is to study the anti-TNBC function of the ethyl acetate extract (EAE) of AF (AF-EAE) and disclose its mechanism of action. MATERIALS AND METHODS: With the aim of elucidating the underlying molecular mechanism and possible chemical basis of AF-EAE in the treatment of TNBC, a comprehensive approach combining system pharmacology and transcriptomic analysis, functional experimental validation, and computational modeling was implemented. Firstly, the potential therapeutic targets of AF-EAE treating TNBC were analyzed by systemic pharmacology and transcriptome sequencing. Subsequently, cell viability assays, cell cycle assays, and transplantation tumor assays were employed to detect the inhibitory effect of AF-EAE on TNBC. Apart from that, the western blot and RT-qPCR assays were adopted to verify its mechanism of action. Finally, the potential chemical basis of anti-TNBC function of AF-EAE was screened through molecular docking and validated by molecular dynamics. RESULTS: This study analyzed the differentially expressed genes after AF-EAE treatment by RNA-sequencing (RNA-seq). It was found that most of the genes were abundant in the gene set termed "cell cycle". Besides, AF-EAE could suppress the proliferation of TNBC cells in vitro and in vivo by inhibiting the function of Skp2 protein. AF-EAE could also lead to the accumulation of p21 and a decrease of CDK6/CCND1 protein, thereby stalling the cycle of cell in the G1/S stage. Notably, clinical data survival analysis clearly demonstrated that Skp2 overexpression has been negatively correlated with survival rates in breast cancer (BC) patients. Further, as suggested by molecular docking and molecular dynamics, the quercetin and its analogues of AF-EAE might bind to Skp2 protein. CONCLUSION: In summary, AF-EAE inhibits the growth of TNBC in vitro and in vivo through targeting Skp2/p21 signaling pathway. While providing a novel potential drug for treating TNBC, this study might establish a method to delve into the action mechanism of TCM.

Curcumol Reduces Aerobic Glycolysis and Overcomes Chemoresistance by Inducing Cdh1-Mediated Skp2 Ubiquitination.

Colorectal cancer (CRC) is the third most common cancer worldwide. The main obstacle in treating advanced CRC is tumor recurrence and metastasis due to chemoresistance. S-phase kinase associated protein 2 (Skp2), an E3 ligase, is highly associated with tumor resistance and a poor prognosis. The results of immunoblotting, immunohistochemical staining, ubiquitination analysis, and co-immunoprecipitation (co-IP) assay revealed that the plant curcuma, curcumol, is a novel Skp2 inhibitor for CRC treatment. Curcumol inhibits aerobic glycolysis in CRC by inducing Skp2 degradation. Co-immunoprecipitation results showed that curcumol enhanced the interaction between cadherin-1 (Cdh1) and Skp2 and led to the ubiquitination and degradation of Skp2. Curcumol exhibited significant antitumor effects against CRC, such as increased intrinsic apoptosis and decreased tumorigenic properties, both in vivo and in vitro. Furthermore, curcumol overcame 5-fluorouracil (5-Fu) resistance in CRC and induced apoptosis in 5-Fu-resistant CRC cells. The present data revealed a novel antitumor mechanism of glycolytic regulation by curcumol, suggesting that curcumol may be a potential chemical candidate for treating 5-Fu-resistant CRC.

Platycodin D suppresses proliferation, migration, and invasion of human glioblastoma cells through regulation of Skp2.

BACKGROUND: Platycodin D (PD) is a major bioactive component of Platycodon grandiflorum, a medicinal herb that is widely used in China, and is effective against various human cancers, including glioblastoma multiforme (GBM). S phase kinase-related protein 2 (Skp2) is oncogenic and overexpressed in various human tumors. It is highly expressed in GBM and its expression is correlated with tumor growth, drug resistance and poor prognosis. In this study, we investigated whether inhibition of glioma progression by PD is mediated by decreasing expression of Skp2. METHODS: Cell Counting Kit-8 (CCK-8) and Transwell assays were used to determine the effects of PD on GBM cell proliferation, migration, and invasion in vitro. mRNA and protein expression were determined by real time polymerase chain reaction (RT-PCR) and western blotting, respectively. The U87 xenograft model was used to verify the anti-glioma effect of PD in vivo. Expression levels of Skp2 protein were analyzed by immunofluorescence staining. RESULTS: PD suppressed proliferation and motility of GBM cells in vitro. The expression of Skp2 in U87 and U251 cells was significantly reduced by PD. PD mainly decreased the cytoplasmic expression of Skp2 in glioma cells. Skp2 protein expression was downregulated by PD, resulting in upregulation of its downstream targets, p21and p27. The inhibitory effect of PD was enhanced by Skp2 knockdown in GBM cells and reversed in cells with Skp2 overexpression. CONCLUSION: PD suppresses glioma development by regulation of Skp2 in GBM cells.

1,25-(OH)2D3/Vitamin D receptor alleviates systemic lupus erythematosus by downregulating Skp2 and upregulating p27.

BACKGROUND: Recent evidence has suggested that the 1,25(OH)2D3/Vitamin D receptor (VDR) acts to suppress the immune response associated with systemic lupus erythematosus (SLE), a serious multisystem autoimmune disease. Hence, the aim of the current study was to investigate the mechanism by which 1,25-(OH)2D3/VDR influences SLE through regulating the Skp2/p27 signaling pathway. METHODS: Initially, the levels of 1,25(OH)2D3, VDR, Skp2, and p27 were measured in collected renal tissues and peripheral blood. Meanwhile, the levels of inflammatory factors, biochemical indicators (BUN, Cr, anti-nRNP IgG, anti-dsDNA IgG) and urinary protein levels were assayed in in VDRinsert and VDR-knockout mice in response to 1,25(OH)2D3 supplement. In addition, the distribution of splenic immune cells was observed in these mice. RESULTS: Among the SLE patients, the levels of 1,25(OH)2D3, VDR and p27 were reduced, while the levels of Skp2 were elevated. In addition, the levels of anti-nRNP IgG and anti-dsDNA IgG were increased, suggesting induction of inflammatory responses. Notably, 1,25(OH)2D3/VDR mice had lower concentrations of BUN and Cr, urinary protein levels, precipitation intensity of the immune complex and complement, as well as the levels of anti-nRNP IgG and anti-dsDNA IgG in SLE mice. Additionally, 1,25(OH)2D3 or VDR reduced the degree of the inflammatory response while acting to regulate the distribution of splenic immune cells. CONCLUSION: This study indicated that 1,25-(OH)2D3/VDR facilitated the recovery of SLE by downregulating Skp2 and upregulating p27 expression, suggesting the potential of 1,25-(OH)2D3/VDR as a promising target for SLE treatment.

Antrodia cinnamomea extract inhibits the proliferation of tamoxifen-resistant breast cancer cells through apoptosis and skp2/microRNAs pathway.

BACKGROUND: Breast cancer is the most common cancer in women and affects 1.38 million women worldwide per year. Antiestrogens such as tamoxifen, a selective estrogen receptor (ER) modulator, are widely used in clinics to treat ER-positive breast tumors. However, remissions of breast cancer are often followed by resistance to tamoxifen and disease relapse. Despite the increasing understanding of the resistance mechanisms, effective regimens for treating tamoxifen-resistant breast cancer are limited. Antrodia cinnamomea is a traditional medicinal mushroom native only to Taiwan. In this study, we aimed to examine in vitro effect of antrodia cinnamomea in the tamoxifen-resistant cancer. METHODS: Antrodia cinnamomea was studied for its biological activity against proliferation of tamoxifen-resistant breast cancer by XTT assay. Next, the underlying mechanism was studied by flow cytometry, qPCR and Western's blotting assay. RESULTS: Our results revealed that the ethanol extract of antrodia cinnamomea (AC) can inhibit the growth of breast cancer cells, including MCF-7 cell and tamoxifen-resistant MCF-7 cell lines. Combination treatment with AC and 10- 6 M tamoxifen have the better inhibitory effect on the proliferation of tamoxifen-resistant MCF-7 cells than only AC did. AC can induce apoptosis in these breast cancer cells. Moreover, it can suppress the mRNA expression of skp2 (S-phase kinase-associated protein 2) by increasing the expressions of miR-21-5p, miR-26-5p, and miR-30-5p in MCF-7 and tamoxifen-resistant MCF-7 cells. CONCLUSIONS: These results suggest that the ethanol extract of antrodia cinnamomea could be a novel anticancer agent in the armamentarium of tamoxifen-resistant breast cancer management. Moreover, we hope to identify additional pure compounds that could serve as promising anti-breast cancer candidates for further clinical trials.

The retinoid X receptor agonist, 9-cis UAB30, inhibits cutaneous T-cell lymphoma proliferation through the SKP2-p27kip1 axis.

BACKGROUND: Bexarotene (Targretin®) is currently the only FDA approved retinoid X receptor (RXR) -selective agonist for the treatment of cutaneous T-cell lymphomas (CTCLs). The main side effects of bexarotene are hypothyroidism and elevation of serum triglycerides (TGs). The novel RXR ligand, 9-cis UAB30 (UAB30) does not elevate serum TGs or induce hypothyroidism in normal subjects. OBJECTIVES: To assess preclinical efficacy and mechanism of action of UAB30 in the treatment of CTCLs and compare its action with bexarotene. METHODS: With patient-derived CTCL cell lines, we evaluated UAB30 function in regulating growth, apoptosis, cell cycle check points, and cell cycle-related markers. RESULTS: Compared to bexarotene, UAB30 had lower half maximal inhibitory concentration (IC50) values and was more effective in inhibiting the G1 cell cycle checkpoint. Both rexinoids increased the stability of the cell cycle inhibitor, p27kip1 protein, in part, through targeting components involved in the ubiquitination-proteasome system: 1) decreasing SKP2, a F-box protein that binds and targets p27kip1 for degradation by 26S proteasome and 2) suppressing 20S proteasome activity (cell line-dependent) through downregulation of PSMA7, a component of the 20S proteolytic complex in 26S proteasome. CONCLUSIONS: UAB30 and bexarotene induce both early cell apoptosis and suppress cell proliferation. Inhibition of the G1 to S cell cycle transition by rexinoids is mediated, in part, through downregulation of SKP2 and/or 20S proteasome activity, leading to increased p27kip1 protein stability. Because UAB30 has minimal effect in elevating serum TGs and inducing hypothyroidism, it is potentially a better alternative to bexarotene for the treatment of CTCLs.

Regulation of Akt/FoxO3a/Skp2 Axis Is Critically Involved in Berberine-Induced Cell Cycle Arrest in Hepatocellular Carcinoma Cells.

The maintenance of ordinal cell cycle phases is a critical biological process in cancer genesis, which is a crucial target for anti-cancer drugs. As an important natural isoquinoline alkaloid from Chinese herbal medicine, Berberine (BBR) has been reported to possess anti-cancer potentiality to induce cell cycle arrest in hepatocellular carcinoma cells (HCC). However, the underlying mechanism remains to be elucidated. In our present study, G0/G1 phase cell cycle arrest was observed in berberine-treated Huh-7 and HepG2 cells. Mechanically, we observed that BBR could deactivate the Akt pathway, which consequently suppressed the S-phase kinase-associated protein 2 (Skp2) expression and enhanced the expression and translocation of Forkhead box O3a (FoxO3a) into nucleus. The translocated FoxO3a on one hand could directly promote the transcription of cyclin-dependent kinase inhibitors (CDKIs) p21Cip1 and p27Kip1, on the other hand, it could repress Skp2 expression, both of which lead to up-regulation of p21Cip1 and p27Kip1, causing G0/G1 phase cell cycle arrest in HCC. In conclusion, BBR promotes the expression of CDKIs p21Cip1 and p27Kip1 via regulating the Akt/FoxO3a/Skp2 axis and further induces HCC G0/G1 phase cell cycle arrest. This research uncovered a new mechanism of an anti-cancer effect of BBR.

Danshen improves survival of patients with colon cancer and dihydroisotanshinone I inhibit the proliferation of colon cancer cells via apoptosis and skp2 signaling pathway.

ETHNOPHARMACOLOGICAL RELEVANCE: Danshen (Salvia miltiorrhiza Bunge) is widely used in traditional Chinese medicine. However, it's definite clinical effect and mechanism on colon carcinoma is unclear. AIM OF THE STUDY: To test the hypothesis that the protective effect of danshen on colon cancer and discover the bioactive compounds through in vitro study. MATERIALS AND METHODS: We conducted a nationwide cohort study by using population-based data from the Taiwan National Health Insurance Research Database (NHIRD). The study cohort comprised patients diagnosed with malignant neoplasm of colon (ICD-9-CM codes:153) in catastrophic illness database between January 1, 2000, and December 31, 2010. We used the Kaplan-Meier method to estimate colon [corrected] cancer cumulative incidences. Next, human colon cancer cells (HCT 116 cells and HT29 cells) were used to investigate the effect of dihydroisotanshinone I (DT) on the proliferation and apoptosis of human colon cancer cells and the underlying mechanism through XTT assay and flow cytometry. The in vivo effect of DT treatment was investigated through a xenograft nude mouse model. RESULTS: In our study, the in vivo protective effect of danshen in the different stage of colon cancer patients was validated through data from the National Health Insurance Research Database in Taiwan. In vitro, we found that dihydroisotanshinone I (DT), a bioactive compound present in danshen, can inhibit the proliferation of colon carcinoma cells, HCT 116 cells and HT-29 cells. Moreover, DT induced apoptosis of colorectal cancer cells. DT also repressed the protein expression of Skp2 (S-Phase Kinase Associated Protein 2) and the mRNA levels of its related gene, Snail1 (Zinc finger protein SNAI1) and RhoA (Ras homolog gene family, member A). In addition, DT also blocked the colon cancer cells recruitment ability of macrophage by decreasing CCL2 secretion in macrophages. DT treatment also significantly inhibited the final tumor volume in a xenograft nude mouse model. CONCLUSION: Danshen has protective effects in colon cancer patients, which could be attributed to DT through blocking the proliferation of colon cancer cells through apoptosis.

Chrysin, Abundant in Morinda citrifolia Fruit Water-EtOAc Extracts, Combined with Apigenin Synergistically Induced Apoptosis and Inhibited Migration in Human Breast and Liver Cancer Cells.

The composition of Morinda citrifolia (M. citrifolia) was determined using high-performance liquid chromatography (HPLC), and the anticancer effects of M. citrifolia extract evaluated in HepG2, Huh7, and MDA-MB-231 cancer cells. M. citrifolia fruit extracts were obtained by using five different organic solvents, including hexane (Hex), methanol (MeOH), ethyl acetate (EtOAc), chloroform (CHCl3), and ethanol (EtOH). The water-EtOAc extracts from M. citrifolia fruits was found to have the highest anticancer activity. HPLC data revealed the predominance of chrysin in water-EtOAc extracts of M. citrifolia fruit. Furthermore, the combined effects of cotreatment with apigenin and chrysin on liver and breast cancer were investigated. Treatment with apigenin plus chrysin for 72-96 h reduced HepG2 and MDA-MB-231 cell viability and induced apoptosis through down-regulation of S-phase kinase-associated protein-2 (Skp2) and low-density lipoprotein receptor-related protein 6 (LRP6) expression. However, the combination treatment for 36 h synergistically decreased MDA-MB-231 cell motility but not cell viability through down-regulation of MMP2, MMP9, fibronectin, and snail in MDA-MB-231 cells. Additionally, chrysin combined with apigenin also suppressed tumor growth in human MDA-MB-231 breast cancer cells xenograft through down-regulation of ki-67 and Skp2 protein. The experimental results showed that chrysin combined with apigenin can reduce HepG2 and MDA-MB-231 proliferation and cell motility and induce apoptosis. It also offers opportunities for exploring new drug targets, and further investigations are underway in this regard.

Equol inhibits prostate cancer growth through degradation of androgen receptor by S-phase kinase-associated protein 2.

Chemopreventive and potential therapeutic effects of soy isoflavones have been shown to be effective in numerous preclinical studies as well as clinical studies in prostate cancer. Although the inhibition of androgen receptor signaling has been supposed as one mechanism underlying their effects, the precise mechanism of androgen receptor inhibition remains unclear. Thus, this study aimed to clarify their mechanism. Among soy isoflavones, equol suppressed androgen receptor as well as prostate-specific antigen expression most potently in androgen-dependent LNCaP cells. However, the inhibitory effect on androgen receptor expression and activity was less prominent in castration-resistant CxR and 22Rv1 cells. Consistently, cell proliferation was suppressed and cellular apoptosis was induced by equol in LNCaP cells, but less so in CxR and 22Rv1 cells. We revealed that the proteasome pathway through S-phase kinase-associated protein 2 (Skp2) was responsible for androgen receptor suppression. Taken together, soy isoflavones, especially equol, appear to be promising as chemopreventive and therapeutic agents for prostate cancer based on the fact that equol augments Skp2-mediated androgen receptor degradation. Moreover, because Skp2 expression was indicated to be crucial for the effect of soy isoflavones, soy isoflavones may be applicable for precancerous and cancerous prostates.

Amino acid sequence motifs essential for P0-mediated suppression of RNA silencing in an isolate of potato leafroll virus from Inner Mongolia.

Polerovirus P0 suppressors of host gene silencing contain a consensus F-box-like motif with Leu/Pro (L/P) requirements for suppressor activity. The Inner Mongolian Potato leafroll virus (PLRV) P0 protein (P0(PL-IM)) has an unusual F-box-like motif that contains a Trp/Gly (W/G) sequence and an additional GW/WG-like motif (G139/W140/G141) that is lacking in other P0 proteins. We used Agrobacterium infiltration-mediated RNA silencing assays to establish that P0(PL-IM) has a strong suppressor activity. Mutagenesis experiments demonstrated that the P0(PL-IM) F-box-like motif encompasses amino acids 76-LPRHLHYECLEWGLLCG THP-95, and that the suppressor activity is abolished by L76A, W87A, or G88A substitution. The suppressor activity is also weakened substantially by mutations within the G139/W140/G141 region and is eliminated by a mutation (F220R) in a C-terminal conserved sequence of P0(PL-IM). As has been observed with other P0 proteins, P0(PL-IM) suppression is correlated with reduced accumulation of the host AGO1-silencing complex protein. However, P0(PL-IM) fails to bind SKP1, which functions in a proteasome pathway that may be involved in AGO1 degradation. These results suggest that P0(PL-IM) may suppress RNA silencing by using an alternative pathway to target AGO1 for degradation. Our results help improve our understanding of the molecular mechanisms involved in PLRV infection.

Korean red ginseng extract induces proliferation to differentiation transition of human acute promyelocytic leukemia cells via MYC-SKP2-CDKN1B axis.

ETHNOPHARMACOLOGICAL RELEVANCE: Korean red ginseng has been used as traditional medicine in East Asia. Recent scientific research revealed multiple effects of Korean red ginseng, including anticancer activity. To evaluate the effect of Korean red ginseng extract (KRGE) in acute promyelocytic leukemia (APL) and elucidate its molecular mechanism. MATERIALS AND METHODS: NB4 cells were treated with 1mg/ml KRGE for 48 h and examined for cell proliferation and differentiation. Cell cycle distribution of KRGE-treated cells was analyzed and the expression level of G1 phase regulators was determined. MYC was overexpressed by retroviral transduction and its effect on SKP2 and CDKN1B gene expression, cell proliferation, cell cycle and differentiation was evaluated in KRGE-treated cells. RESULTS: KRGE alone was sufficient to induce granulocytic differentiation accompanied with growth inhibition. KRGE treatment resulted in cell cycle arrest at the G1 phase with augmented Cdkn1b proteins without changes in transcript levels. Cycloheximide treatment revealed reduced degradation of Cdkn1b protein by KRGE. In addition, KRGE treatment reduced expression of MYC and SKP2 genes, both at mRNA and protein levels. Upon ectopic expression of MYC, the effect of KRGE was reversed with lesser reduction and induction of SKP2 gene and Cdkn1b protein, respectively. Taken together, these results suggest a sequential molecular mechanism from MYC reduction, SKP2 reduction, Cdkn1b protein stabilization, G1 phase arrest to granulocytic differentiation by KRGE in human APL. CONCLUSIONS: KRGE induces leukemic proliferation to differentiation transition in APL through modulation of the MYC-SKP2-CDKN1B axis.

Identification of a canonical SCF(SLF) complex involved in S-RNase-based self-incompatibility of Pyrus (Rosaceae).

S-RNase-based self-incompatibility (SI) is an intraspecific reproductive barrier to prevent self-fertilization found in many species of the Solanaceae, Plantaginaceae and Rosaceae. In this system, S-RNase and SLF/SFB (S-locus F-box) genes have been shown to control the pistil and pollen SI specificity, respectively. Recent studies have shown that the SLF functions as a substrate receptor of a SCF (Skp1/Cullin1/F-box)-type E3 ubiquitin ligase complex to target S-RNases in Solanaceae and Plantaginaceae, but its role in Rosaceae remains largely undefined. Here we report the identification of two pollen-specific SLF-interacting Skp1-like (SSK) proteins, PbSSK1 and PbSSK2, in Pyrus bretschneideri from the tribe Pyreae of Rosaceae. Both yeast two-hybrid and pull-down assays demonstrated that they could connect PbSLFs to PbCUL1 to form a putative canonical SCF(SLF) (SSK/CUL1/SLF) complex in Pyrus. Furthermore, pull-down assays showed that the SSK proteins could bind SLF and CUL1 in a cross-species manner between Pyrus and Petunia. Additionally, phylogenetic analysis revealed that the SSK-like proteins from Solanaceae, Plantaginaceae and Rosaceae form a monoclade group, hinting their shared evolutionary origin. Taken together, with the recent identification of a canonical SCF(SFB) complex in Prunus of the tribe Amygdaleae of Rosaceae, our results show that a conserved canonical SCF(SLF/SFB) complex is present in Solanaceae, Plantaginaceae and Rosaceae, implying that S-RNase-based self-incompatibility shares a similar molecular and biochemical mechanism.

Identification of a Skp1-like protein interacting with SFB, the pollen S determinant of the gametophytic self-incompatibility in Prunus.

Many species in Rosaceae, Solanaceae, and Plantaginaceae exhibit S-RNase-based self-incompatibility (SI). In this system, the pistil and pollen specificities are determined by S-RNase and the S locus F-box protein, respectively. The pollen S determinant F-box protein in Prunus (Rosaceae) is referred to by two different terms, SFB (for S-haplotype-specific F-box protein) and SLF (for S locus F box), whereas it is called SLF in Solanaceae and Plantaginaceae. Prunus SFB is thought to be a molecule indispensable for its cognate S-RNase to exert cytotoxicity and to arrest pollen tube growth in incompatible reactions. Although recent studies have demonstrated the molecular function of SCF(SLF) in the SI reaction of Solanaceae and Plantaginaceae, how SFB participates in the Prunus SI mechanism remains to be elucidated. Here we report the identification of sweet cherry (Prunus avium) SFB (PavSFB)-interacting Skp1-like1 (PavSSK1) using a yeast (Saccharomyces cerevisiae) two-hybrid screening against the pollen cDNA library. Phylogenetic analysis showed that PavSSK1 belongs to the same clade as Antirrhinum hispanicum SLF-interacting Skp1-like1 and Petunia hybrida SLF-interacting Skp1-like1 (PhSSK1). In yeast, PavSSK1 interacted not only with PavSFBs from different S haplotypes and Cullin1-likes (PavCul1s), but also with S-locus F-box-likes. A pull-down assay confirmed the interactions between PavSSK1 and PavSFB and between PavSSK1 and PavCul1s. These results collectively indicate that PavSSK1 could be a functional component of the SCF complex and that PavSFB may function as a component of the SCF complex. We discuss the molecular function of PavSFB in self-/nonself-recognition in the gametophytic SI of Prunus.

Vasoactive intestinal peptide decreases MYCN expression and synergizes with retinoic acid in a human MYCN-amplified neuroblastoma cell line.

Neuroblastoma is a pediatric tumor which can spontaneously regress or differentiate into a benign tumor. MYCN oncogene amplification occurs in 22% of neuroblastomas and is associated with poor prognosis. Retinoic acid (RA), a molecule able to induce differentiation and to decrease MYCN expression, is used in the therapy of neuroblastomas. The neuropeptide vasoactive intestinal peptide (VIP) is known to control proliferation or differentiation of numerous cancer cells. In vitro, VIP induces differentiation of neuroblastoma cells. To determine whether VIP could modulate MYCN expression, we carried out real-time quantitative RT-PCR and Western immunoblot analyses in human neuroblastoma SH-SY5Y and IMR-32 cells. The results indicated that VIP reduced MYCN mRNA and protein expression, especially in the MYCN-amplified IMR-32 cells, with a maximal and transient decrease by approximately 50% after few hours of treatment with VIP at 10(-6) M. This effect was compared to that of RA at 10(-5) M, which induced a diminution of MYCN mRNA expression by approximately 25% after few days of treatment. This indicated that VIP and RA display complementary kinetics. Cotreatments showed that VIP and RA had synergistic effects on regulation of expression of MYCN proteins. VIP and RA cotreatments regulated also expression of two MYCN target genes, SKP2 and TP53INP1. These results suggest that VIP, in combination with RA may have a potential therapeutic benefit in neuroblastomas with MYCN amplification, a genetic abnormality associated with poor prognosis.

AhSSK1, a novel SKP1-like protein that interacts with the S-locus F-box protein SLF.

The S-locus F-box (SLF/SFB) protein, recently identified as the pollen determinant of S-RNase-based self-incompatibility (SI) in Solanaceae, Scrophulariaceae and Rosaceae, has been proposed to serve as the subunit of an SCF (SKP1-CUL1-F-box) ubiquitin ligase and to target its pistil counterpart S-RNase during the SI response. However, the underlying mechanism is still in dispute, and the putative SLF-binding SKP1-equivalent protein remains unknown. Here, we report the identification of AhSSK1, Antirrhinum hispanicumSLF-interacting SKP1-like1, using a yeast two-hybrid screen against a pollen cDNA library. GST pull-down assays confirmed the SSK1-SLF interaction, and showed that AhSSK1 could connect AhSLF to a CUL1-like protein. AhSSK1, despite having a similar secondary structure to other SKP1-like proteins, appeared quite distinctive in sequence and unique in a phylogenetic analysis, in which no SSK1 ortholog could be predicted in the sequenced genomes of Arabidopsis and rice. Thus, our results suggest that the pollen-specific SSK1 could be recruited exclusively as the adaptor of putative SCF(SLF) in those plants with S-RNase-based SI, providing an important clue to dissecting the function of the pollen determinant.