The MEK/ERK and PI3K/AKT signaling pathways modulate cell growth and apoptosis resistance induced by PKCd overexpression in normal murine mammary cells

VALERIA C. GROSSONI; JUAN KARLIC; MARCELO G. KAZANIETZ; ELISA D. BAL DE KIER JOFFÉ; ALEJANDRO J. URTREGER

Los Angeles, EEUU.

Congreso; 98th Annual Meeting of the American Associaton for Cancer Research; 2007

American Associaton for Cancer Research (AACR)

PKCs constitute a serin-threonin kinase family that controls many cell functions as growth, differentiation and malignant transformation. In the present work, we have studied whether PKCd (delta) overexpression could modulate proliferation and survival capacities of normal murine mammary cells (NMuMG), two phenomena closely related with the development of a malignant phenotype. Under constitutive conditions, PKCd overexpression induced a slight increase in proliferative capacity. However, upon PMA activation (50 nM, 1h) a significant increase in the proliferative capacity could be detected by flow cytometry and [3H]-Thy incorporation (p< 0.05 vs. control cells). Increased proliferation was associated with ERK activation, a rise in cyclin D1 expression (3.5 times, p< 0.01) and in Rb phosphorylation (2.4 times, p< 0.05). In addition, cell cycle inhibitors p21 and p27 showed an important downmodulation after PKCd activation. To confirm a straight relation between PKCd and MEK/ERK pathway activation, endogenous PKCd expression was knocked down by RNA interference. Under these conditions, an important reduction in pERK levels (80%; p< 0.05), could be detected. Furthermore, NMuMG-PKCd cells were more resistant to cell death induced by serum starvation or cytotoxic drugs (doxorubicin) than vector transfected cells (increase in survival: 25% to 50% vs. control cells, p< 0.05). The treatment with pharmacological inhibitors of MEK/ERK (PD98059) and PI3K/Akt (LY94002) indicated that PI3K/Akt signalling pathway was the responsible for the higher apoptosis resistance. Under constitutive conditions, a low expression of PKCd could be found in the mitochondrial fraction by Western blot, but 15 min after PMA treatment an increase in PKCd traslocation to mitochondria could be observed in NMuMG-PKCd cells. The involvement of this phenomenon on cell survival is still unknown. The overexpression of PKCd in NMuMG cells was also associated with the acquisition of an anchorage-independent growth capacity.Contrarily to other cell models, PKCd seems to be favoring breast carcinogenesis by controlling growth and apoptosis resistance through the modulation of two independent signaling pathways MEK/ERK and PI3K/Akt respectively.