Vav1 downmodulates Akt in different breast cancer subtypes: a new promising chance to improve breast cancer outcome

Abstract

Targeting different members of the Akt pathways is a promising therapeutic chance in solid tumors including breast cancer. The variable expression levels of Akt isoforms with opposite effects on tumor growth and metastasis, however, make it difficult to select the inhibitors to be used for specific breast tumor subtypes. Using in vitro and in vivo models, we demonstrated here that Vav1, ectopically expressed in invasive breast tumors derived cells, downmodulates Akt acting at expression and/or activation levels depending on tumor subtype. The decreased p‐Akt1 (Ser473) levels are a common effect of Vav1 upmodulation, suggesting that, in breast tumor‐derived cells and independently of their phenotype, Vav1 interferes with signaling pathways ended to specifically recruit Akt1. Only in ER‐negative cell lines, the silencing of Vav1 induced the expression but not the activation of Akt2. A retrospective analysis of early invasive breast tumors allowed to establish the prognostic significance of the p‐Akt/Vav1 relationship. In particular, low Vav1 levels negatively influence the follow‐up of patients with low p‐Akt in their primary tumors and subjected to adjuvant chemotherapy. As the use of specific or pan Akt inhibitors may not be sufficient or may even be detrimental, increasing the levels of Vav1 could be a new approach to improve breast cancer outcomes. This might be particularly relevant for tumors with a triple‐negative phenotype, for which target‐based therapies are not currently available.

Vav1 Down-Modulates Akt2 Expression in Cells from Pancreatic Ductal Adenocarcinoma: Nuclear Vav1 as a Potential Regulator of Akt Related Malignancy in Pancreatic Cancer

“…Despite its reported role as a negative prognostic molecule [ 25 ], in breast tumor cells, Vav1 down-modulates the activation status of Akt1, independently from tumor phenotypes, and reduces the expression of Akt1 in cells with an ER+ phenotype. Furthermore, the silencing of Vav1 in ER− cells induced the expression, but not the activation, of Akt2 [ 7 ].…”

“…Silencing of Vav1 in HPAF-2 and HPAC cells and Vav1 over-expression in HPAF-2, HPAC, and PL-45 cell lines were performed with 1mg/mL Lipofectamine 2000 (Thermo Fisher Scientific, Waltham, MA, USA), essentially following previously reported procedures [ 7 ]. In particular, the down-modulation of Vav1 was performed by silencing protein with specific siRNAs (Santa Cruz Biotechnology, Santa Cruz, CA, USA) and Vav1 over-expression was obtained by transient transfection with a pEF plasmid expressing the human full-length Vav1.…”

“…For Western blot analysis, total lysates (50 μg protein) from cells under different experimental conditions were separated on 8.5% polyacrylamide denaturing gels and blotted into nitrocellulose membranes (GE Healthcare Life Science, Little Chalfont, UK). Membranes were reacted with antibodies directed against Vav1 (sc-8039) , p-Akt1/2/3 (sc-14032), Akt1 (sc-1618), and Akt2 (sc-5270), all purchased from Santa Cruz Biotechnology (Santa Cruz Biotechnology), and against β-tubulin, as previously reported [ 7 ]. Membranes were then incubated with peroxidase-conjugated secondary antibodies, and the immunocomplexes were detected by chemiluminescence using the ECL system (Perkin Elmer, Boston, MA, USA).…”

“…In cells from invasive breast tumors, we have recently demonstrated that activation and/or expression of specific Akt isoforms can be down-regulated by Vav1 [ 7 ], a multidomain protein physiologically expressed only in hematopoietic cells, in which it participates in cytoskeleton reorganization and gene transcription [ 8 ]. Vav1 is ectopically expressed in a number of non-hematopoietic cancers, including PDAC [ 9 ], in which this protein seems to be involved in signal transduction processes correlated with aggressive tumor phenotypes [ 10 , 11 , 12 ].…”

“…Considering that nuclear Vav1 is involved in gene transcription in myeloid leukemia cells [ 14 , 15 ] and that, in breast tumor cells, Vav1 plays a phenotype-related role in down-modulating the expression of specific Akt isoforms [ 7 ], the aim of this work was to establish whether Vav1 has a role in down-regulating the Akt pathway in pancreatic ductal adenocarcinoma. We found that the accumulation of Vav1 inside the nucleus inversely correlates with Akt2 expression in both PDAC-derived cells and pancreatic tumor tissues.…”