TGFß engages MEK/ERK to differentially regulate benign and malignant pancreas cell function.

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

Conformational properties of five peptides corresponding to the entire sequence of glutathione transferase domain II.

Five peptides matching the helices alpha4, alpha5, alpha6, alpha7, and alpha8, spanning the entire sequence of domain II of pG-STP1-1, have been synthesized and their conformations analyzed by far-UV CD spectroscopy. The results show that a5, a7, and a8 peptides are unstructured in water/2,2,2-trifluoroethanol (TFE) solutions. The a4-peptide also adopts random conformations in aqueous solvent. Moreover, the relative low helical content (20%), estimated for this peptide in the presence of 30% (v/v) TFE, suggests that the sequence of this protein fragment does not possess sufficient information for a strong helical propensity. On the contrary, the synthesized a6 peptide, in the presence of TFE, showed a relevant structural autonomy with a helical content (41%) which was significantly higher than that estimated, under the same conditions, for all other peptides. More in general in the presence of solvents less polar than water, the isolated a6 peptide shows the same helical conformation adopted by the corresponding alpha6-helix in the hydrophobic core of the protein. A n-capping box motif, strictly conserved at the N-terminal of the alpha6-helix of all GST and related protein including eucaryotic translation elongation factor (EF1gamma) and the yeast prion protein Ure2, plays an important role in the alpha-helix nucleation and stability of this protein fragment. The results suggest that the alpha6-helix might represent a nucleation site of GST folding and that the helical conformation of this region of the protein is an important requirement during earlier events of GST refolding.

Structural characterization of acid-induced intermediates of human glutathione transferase P1-1.

The acid denaturation of human glutathione transferase P1-1 (hGSTP1-1) has been performed to investigate the unfolding intermediates of the protein and their possible involvement in the refolding mechanism. The acid-induced structures of GSTP1-1 have been characterized by activity, gel filtration, intrinsic fluorescence and far-u.v. circular dichroism (CD) techniques. Because of the non-identity of the different transitions monitored, the acid denaturation of hGSTP1-1 appears to be a multistep process during which several intermediates coexist in equilibrium. The dependence of inactivation on the protein concentration, as well as gel-filtration experiments, indicate that the inactivation transition, centred at about pH 4.0, corresponds to the monomerization of the protein. At pH 2.0, when the enzyme is completely inactive, the protein retains a small, but significant, amount of secondary structure. This means that the dimeric arrangement of the molecule is important for maintaining the native-like secondary structure of the monomer. The results show that, at low pH, the compact state of the GST monomer, even upon the addition of salts, does not possess native-like secondary structure as described for many monomeric proteins (molten globule). In the presence of physiological concentrations of salts, the protein solution at pH 2.0 leads to a dead-end aggregation process, suggesting that this compact state cannot represent a productive intermediate of the refolding pathway.