p130Cas scaffold protein regulates ErbB2 stability by altering breast cancer cell sensitivity to autophagy.

Overexpression of the ErbB2/HER2 receptor tyrosine kinase occurs in up to 20% of human breast cancers and correlates with aggressive disease. Several efficacious targeted therapies, including antibodies and kinase inhibitors, have been developed but the occurring of resistance to these agents is often observed. New therapeutic agents targeting the endocytic recycling and intracellular trafficking of membrane in tumor cells overexpressing ErbB2 are actually in clinical development. Nevertheless the mechanisms underlying ErbB2 downregulation are still obscure. We have previously demonstrated that the overexpression of the p130Cas adaptor protein in ErbB2 positive breast cancer, promotes tumor aggressiveness and progression. Here we demonstrate that lowering p130Cas expression in breast cancer cells is sufficient to induce ErbB2 degradation by autophagy. Conversely, p130Cas overexpression protects ErbB2 from degradation by autophagy. Furthermore, this autophagy-dependent preferential degradation of ErbB2 in absence of p130Cas is due to an increased ErbB2 ubiquitination. Indeed, the overexpression of p130Cas impairs ErbB2 ubiquitination by inhibiting the binding of Cbl and CHIP E3 ligases to ErbB2. Finally, our results indicate that p130Cas-dependent ErbB2 protection from degradation by autophagy may alter the sensitivity to the humanized monoclonal antibody trastuzumab. Consistently, in human ErbB2 positive breast cancers that develop resistance to trastuzumab, p130Cas expression is significantly increased suggesting that elevated levels of p130Cas can be involved in trastuzumab resistance.

New alternative splicing BCR/ABL-OOF shows an oncogenic role by lack of inhibition of BCR GTPase activity and an increased of persistence of Rac activation in chronic myeloid leukemia.

In Chronic Myeloid Leukemia 80% of patients present alternative splice variants involving BCR exons 1, 13 or 14 and ABL exon 4, with a consequent impairment in the reading frame of the ABL gene. Therefore BCR/ABL fusion proteins (BCR/ABL-OOF) are characterized by an in-frame BCR portion followed by an amino acids sequence arising from the out of frame (OOF) reading of the ABL gene. The product of this new transcript contains the characteristic BCR domains while lacking the COOH-terminal Rho GTPase GAP domain. The present work aims to characterize the protein functionality in terms of cytoskeleton (re-)modelling, adhesion and activation of canonical oncogenic signalling pathways. Here, we show that BCR/ABL-OOF has a peculiar endosomal localization which affects EGF receptor activation and turnover. Moreover, we demonstrate that BCR/ABL-OOF expression leads to aberrant cellular adhesion due to the activation of Rac GTPase, increase in cellular proliferation, migration and survival. When overexpressed in a BCR/ABL positive cell line, BCR/ABL-OOF induces hyperactivation of Rac signaling axis offering a therapeutic window for Rac-targeted therapy. Our data support a critical role of BCR/ABL-OOF in leukemogenesis and identify a subset of patients that may benefit from Rac-targeted therapies.