Influence Of TGF-β On Fibroblasts In Tumor-stroma Interactions Of Colorectal Carcinoma

Colorectal carcinoma is one of the most malignant tumors that threaten our health and reduce our life quality. Though the therapy developed with time, the mortality of colorectal carcinoma is still stubbornly high, owing to the high recurrence rate and drug resistance. As other kinds of tumors, colorectal carcinoma progression was also accompanied by abundant activated extracellular matrix (ECM) deposition which is also named'desmoplasia'. Fibroblasts play important role during this process. Fibroblasts in tumor stroma acquire activated phenotype with abundant a-SMA expression, enhanced growth factors secreting potential and increased deposition and remodeling of ECM. Activated fibroblasts in tumor stroma is also termed peritumoral fibroblasts, reactive stromal fibroblasts, cancer associated fibroblasts or tumor-associated fibroblasts.Fibroblasts play its role in tumorigenesis through tumor-stroma interactions. Related articles showed that cancer-associated fibroblasts can promote tumor initiation and metastasis, and in our previous study we also found that tumor cell-fibroblast coculture accelerated tumor cells proliferation, but how tumor cells influence fibroblasts is little explored. In this experiment, we investigated the influence of colorectal cancer cell line SW620 on human embryo lung fibroblast (HELF) including proliferation, apoptosis and senescence by using two layers coculture and conditioned media coculture. Our results showed that the conditioned media of SW620 cells promote proliferation of HELF cells but inhibit its apoptosis and senescence. We suppose that enhanced proliferation ability of fibroblast induced by tumor cells may be the basis of desmoplasia. Through it, tumor cells promote ECM disposition and finally influence the prognosis of the patients. Tumor-stroma interactions also induce gene changes of fibroblasts. In our previous study, we demonstrated that tumor-stroma coculture enhances IGFBP7 expression in tumor cells, and in this experiment we proceed to explore the change of IGFBP7 expression in fibroblasts cells and its associated factors. RT-PCR results show that IGFBP7 expression increased in. HELF cells when coutured with SW620 cells conditioned media.TGF-βsignaling is one of the most important pathways in tumor-stroma interactions. Tumor cells and fibroblasts interact with each other by paracrine growth factors like TGF-βand the interactions influence tumor progression. Is the phenomenon we observed in our experiment that conditioned media of SW620 cells promote proliferation but inhibit apoptosis and senescence of HELF cells induced by TGF-β? To explore the mechanism, we first detected the TGF-βexpression of some colorectal cancer cells and fibroblasts in our lab using RT-PCR, and we found that a certain level of TGF-βwas expressed in colorectal cancer cell lines SW620,SW480,RKO, but not in HELF cells. And then, we cocultured SW620 cells with HELF cells. The two kinds of cells were seeded on the upper layer or the lower layer separately without contact, but the culture media of them can interact through the millipore of the transwell. This coculture system imitates the tumor-stroma interaction well. The results showed that TGF-βexpression of SW620 cells was enhanced when cocultured with HELF cells. Further experiments also showed that HELF cells treated by exogenous TGF-βproduced to be the same results as in conditioned media of SW620 cells. Enhanced IGFBP7 expression also can be induced by exogenous TGF-βsimilarly. But how TGF-βinfluence IGFBP7 expression in HELF cells during tumor-stroma interactions and what's the consequence of enhanced IGFBP7 expression in fibroblasts need further exploration.All above results indicate that tumor-stroma interactions are very sophisticated. Tumor cells secrete some factors and promote fibroblasts activation. Actived fibroblasts may enhance the growth factor secretion of tumor cells and conversely influence fibroblasts behavior themselves.From the above findings, we can get the following conclusions:1. Tumor cells promote IGFBP7 expression and proliferation of fibroblasts but inhibit its apoptosis and senescence.2. TGF-P promote IGFBP7 expression of fibroblasts and inhibit its apoptosis and senescence.3. Tumor-stroma interactions promote TGF-P expression in tumor cells, which indicate that effect of tumor cells on fibroblasts may be mediated by TGF-βpathway.