Abstract 1199: Implications of protein kinase C (PKC)α and PKCΔ on murine mammary tumor growth and metastatic dissemination; effect of retinoids

Abstract

Abstract The retinoid system exerts some of its effects on cell differentiation and malignant phenotype reversion through the interaction of its receptors (RAR) with different PKC isoforms. In this work, using a murine mammary tumor cell line (LM3), we studied the interaction between RARs and PKC in vitro as well as whether the overexpression of α and Δ PKC isoforms could influence the effect of retinoids on cell proliferation both in vivo and in vitro. Western blot assays showed that the pharmacological inhibition of PKCΔ (Rottlerin 5μM, 24h) impaired all trans retinoic acid (ATRA)-induced RARα1 translocation to the nucleus while the pharmacological inhibition of PKCα (Gö6976 5μM, 24h) did not affect this translocation. Moreover, immunoprecipitation assays showed that only PKCΔ co-immunoprecipitated with RARα1 after ATRA treatment, suggesting a physical interaction between both molecules. However, both PKC isoforms seemed to be necessary for RARs activation as determined by a gene reporter assay. Next, by a stable transfection procedure, we overexpressed PKCα and PKCΔ in LM3 cell line. In vitro assays showed that LM3-PKCα cells presented the highest proliferative rate and were highly responsive to ATRA treatment reducing their growth capability. These genetically modified lines were also inoculated orthotopically into the mammary glands of female BALB/c mice. Ten days later, when tumors were palpable, mice were implanted with ATRA pellets (10 mg/mouse). Tumors overexpressing PKCα presented a higher growth rate and were more metastatic than control vector-transfected LM3 cells, but showed a significant response to ATRA treatment, impairing primary tumor growth and reducing lung metastases number [Md (range) 55 (20-75) vs. 16 (0-27) in non-treated and ATRA-treated LM3-PKCα cells respectively (P<0.05 Mann-Whitney test)]. Both control and PKCΔ overexpressing tumors were unresponsive to retinoid treatment.We can conclude that, while PKCα overexpressing cells were more aggressive than control ones, they showed an important response to retinoid treatment both in vivo and in vitro, indicating that a retinoid therapy could be successful in human mammary tumors with high PKCα levels. On the other hand, while we found an in vitro clear interaction between PKCΔ and RARα1, the overexpression of PKCΔ did not to modulate their response to the retinoid therapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1199. doi:10.1158/1538-7445.AM2011-1199