While pancreatic cancer accounts for only 2.8% of new cancer cases each year in the United States, it is projected to be the third leading cause of cancer-related mortality by the end of 2016. Combined, these data suggest that during carcinogenesis pERK initially facilitates and later antagonizes TGFβ-mediated cell cycle arrest, yet remains critical for the pathological, EMT-inducing arm of TGFβ signaling. Furthermore, inhibition of pERK both reduced levels of CDK2 and prevented EMT independent of exogenous TGFβ, consistent with most observations identifying pERK as a tumor promoter.
In cancer cells, pERK had no effect on TGFβ-induced upregulation of pSMAD2 and p21, suggesting the two pathways have completely diverged with respect to the cell cycle. In neoplastic PanIN cells, pERK was not necessary for either TGFβ-induced pSMAD2 phosphorylation or CDK2 repression, but was required for upregulation of p21 and EMT indicating a partial divergence between TGFβ and MEK/ERK in early carcinogenesis. These observations suggest that ERK is a key factor in growth suppressive TGFβ signals, yet may also contribute to detrimental TGFβ signaling such as EMT. Similar to results that our group has published in colon cancer cells, inhibition of ERK phosphorylation in duct cells mitigated TGFβ-induced upregulation of growth suppressive pSMAD2 and p21, prevented downregulation of the pro-growth signal CDK2 and ablated TGFβ-induced EMT. Furthermore, exogenous TGFβ led to rapid and sustained TGFBR1-dependent ERK phosphorylation in benign pancreatic duct cells. These models displayed reduced levels of pERK irrespective of KRAS mutation. To better understand dysregulation of the TGFβ pathway, we first generated mouse models of neoplastic disease with TGFβ receptor deficiencies. While TGFβ signals are anti-proliferative in benign and well-differentiated pancreatic cells, TGFβ appears to promote the progression of advanced cancers.
0 kommentar(er)
