The scaffolding protein, hematopoietic PBX-interacting protein (HPIP/PBXIP1), regulates cell migration necessary for cancer cell dissemination. However, the mechanism that governs this process remains unknown. We show here that HPIP expression is associated with stages of breast cancer where cell dissemination results in poor patient outcome. Our investigation finds a novel association of HPIP with focal adhesion kinase (FAK) regulating FA dynamics. Interestingly, this interaction that led to activation of FAK protein was mediated by the C-terminal domain of HPIP and not the typical integrin-binding motif. Further, short hairpin RNA-mediated knockdown of FAK expression significantly reduced HPIP-induced cell migration indicating participation of FAK pathway. Live-cell time-lapse imaging and biochemical analysis further established the role of HPIP in microtubule-induced FA disassembly. We also found that HPIP-mediated MAPK activation led to phosphorylation and subsequent activation of calpain2, and the activated calpain2 in turn proteolyses FA protein, talin. Interestingly, HPIP is also proteolysed by calpain2 in breast cancer cells. The proteolysis of HPIP and talin by calpain2, and the activation of calapin2 by HPIP-mediated MAPK phosphorylation, is a novel regulatory axis to modulate the cell migration signal. Together, we have determined HPIP as a novel activator of FAK and a new substrate of calpain2. These molecular interactions between HPIP and FAK, and HPIP and calpain2 regulate cell adhesion and migration through modulation of FA dynamics.
BackgroundSmurf2 is a member of the HECT family of E3 ubiquitin ligases that play important roles in determining the competence of cells to respond to TGF- β/BMP signaling pathway. However, besides TGF-β/BMP pathway, Smurf2 regulates a repertoire of other signaling pathways ranging from planar cell polarity during embryonic development to cell proliferation, migration, differentiation and senescence. Expression of Smurf2 is found to be dysregulated in many cancers including breast cancer. The purpose of the present study is to examine the effect of Smurf2 knockdown on the tumorigenic potential of human breast cancer cells emphasizing more on proliferative signaling pathway.MethodssiRNAs targeting different regions of the Smurf2 mRNA were employed to knockdown the expression of Smurf2. The biological effects of synthetic siRNAs on human breast cancer cells were investigated by examining the cell proliferation, migration, invasion, focus formation, anchorage-independent growth, cell cycle arrest, and cell cycle and cell proliferation related protein expressions upon Smurf2 silencing.ResultsSmurf2 silencing in human breast cancer cells resulted in a decreased focus formation potential and clonogenicity as well as in vitro cell migration/invasion capabilities. Moreover, knockdown of Smurf2 suppressed cell proliferation. Cell cycle analysis showed that the anti-proliferative effect of Smurf2 siRNA was mediated by arresting cells in the G0/G1 phase, which was caused by decreased expression of cyclin D1and cdk4, followed by upregulation p21 and p27. Furthermore, we demonstrated that silencing of Smurf2 downregulated the proliferation of breast cancer cells by modulating the PI3K- PTEN-AKT-FoxO3a pathway via the scaffold protein CNKSR2 which is involved in RAS-dependent signaling pathways. The present study provides the first evidence that silencing Smurf2 using synthetic siRNAs can regulate the tumorigenic properties of human breast cancer cells in a CNKSR2 dependent manner.ConclusionsOur results therefore suggest a novel relation between Smurf2 and CNKSR2 thereby regulating AKT-dependent cell proliferation and invasion. Owing to the fact that PI3K-AKT signaling is hyperactivated in various human cancers and that Smurf2 also regulates cellular transformation, our results indicate that Smurf2 may serve as a potential molecule for targeted cancer therapy of certain tumour types including breast cancer.
Background Solanum nigrum, herbal plant that commonly grows in temperate climate zone, has been used as a traditional folk medicine whose ripen fruits were proven to exhibit anti-tumor properties. In traditional Chinese medicine, it has been used for centuries to cure inflammation, edema, mastitis and hepatic cancer and in the Ayurvedic system of traditional medicine in India, S. nigrum is applied against enteric diseases, ulcer, diarrhea and skin diseases. A methanolic glycosidic extract fraction of unripe fruit of S. nigrum (SNME) was investigated for its anticancer property and possible mechanism to surmount adriamycin resistance in NCI/ADR-RES cells.MethodsThe NCI/ADR-RES cells were treated with 7.8125, 15.625, 31.25, 62.5, 125 and 250 μg/ml of methanolic extract of S. nigrum (SNME) for 12, 24 and 48 h, to check the cell viability and proliferation. The cells were also exposed to adriamycin alone or in combination with SNME and the effects on cell growth were determined by MTT. Cell cycle analysis, Ethidium bromide and Acridine orange staining, Annexin-binding efficiency, nuclear condensation and DNA fragmentation of the apoptotic NCI/ADR-RES cells were also determined. To elucidate the relationship between SNME and multi drug resistance, we analyzed the expression levels of Mdr-1, JAK1, STAT3, and pSTAT3 in NCI/ADR-RES cells after treatment with SNME.ResultsResults from the cytotoxicity assay showed a direct correlation between the concentration of methanolic glycosidic extract fraction of S. nigrum (SNME) and the surviving cell population. Combination with Adriamycin, SNME exhibits a synergistic action on NCI/ADR-RES cells, giving the first line of evidence to overcoming Adriamycin resistance. The SNME mediated cell growth suppression was proven to be apoptotic, based on results obtained from DNA fragmentation, annexin V apoptosis assaay and PARP cleavage analysis. Looking into the molecular insight SNME surpasses the chemoresistance of NCI/ADR-RES cells by inhibiting the JAK-STAT3 signaling pathway through the down regulation of JAK1, STAT3, pSTAT3, and Mdr1 expression.ConclusionsCollectively our findings suggest that unripe fruit of Solanum nigrum could possibly be used as a chemosensitizing agent against Adriamycin resistant cancers.
BackgroundSignal transducer and activator of transcription 3 (STAT3) is a key signaling molecule and a central cytoplasmic transcription factor, implicated in the regulation of growth. Its aberrant activation has been demonstrated to correlate with many types of human malignancy. However, whether constitutive STAT3 signaling plays a key role in the survival and growth of soft-tissue tumors is still unclear and hence needs to be elucidated further. In our study we examined the expression levels of STAT3 and pSTAT3 in different grades of soft tissue tumors and correlated with its clinicopathological characteristics.MethodsExpression levels of STAT3 and pSTAT3 in soft tissue tumors were studied using Immunohistochemistry, Western blotting and Reverse transcriptase- PCR and correlated with its clinicopathological characteristics using Chi squared or Fisher's exact test and by logistic regression analysis. Statistical analysis was done using Intercooled Stata software (Intercooled Stata 8.2 version).ResultsOf the 82 soft tissue tumor samples, fifty four (65.8%) showed immunoreactivity for STAT3 and twenty eight (34.1%) for pSTAT3. Expression of STAT3 and pSTAT3 was significantly associated with tumor grade (P < 0.001; P < 0.001), tumor location (P = 0.025; P = 0.027), plane of tumor (P = 0.011; P = 0.006), and tumor necrosis (P = 0.001; P = 0.002). Western blotting and RT-PCR analysis showed increased expression of STAT3 and p-STAT3 as grade of malignancy increased. ConclusionThese findings suggest that constitutive activation of STAT3 is an important factor related to carcinogenesis of human soft tissue tumors and is significantly associated with its clinicopathological parameters which may possibly have potential diagnostic implications.
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