The treatment with all trans retinoic acid (ATRA) modulates the expression of alpha (a) and delta (d) protein kinase C (PKC) isoforms and induces growth inhibition in human and murine mammary cell lines

ALEJANDRO J. URTREGER; DAMIAN E. BERARDI; MARÍA INÉS DÍAZ BESSONE; ELISA D. BAL DE KIER JOFFÉ; LAURA B. TODARO

Denver

Congreso; 100th Annual Meeting of the American Associaton for Cancer Research; 2009

American Associaton for Cancer Research (AACR)

ATRA is the main active metabolite of vitamin A. Its genomic mechanism of action involves the formation of complexes with nuclear receptors (RARs) favoring or inhibiting the expression of target genes, and exerting different biological effects related to growth, differentiation and cell death. It was recently described a non genomic mechanism of action based on the interaction with different signal transduction pathways that could involve the PKC ones. PKC is a serine-threonine kinase family that controls many cell functions including, malignant transformation and metastatic dissemination. PKCa is a classical isoform since it is activated by Ca++ and diacilglycerol (DAG) whereas PKCd is a novel isoform since it is activated by DAG but it is Ca++ insensitive. Some evidences indicate that PKCd may regulate the expression of some retinoid acid (RA) dependent genes, and others indicate that retinoids could alter PKCa intracellular localization; both processes would lead to cell differentiation. We used the murine mammary cell lines LM3 (tumor derived) and NMuMG (normal) and the human tumor-derived cell line MDA-MB231, in order to explore and characterize the crosstalk between RA and PKC signaling pathways. While the treatment with PMA (50 nM) induced a marked reduction in the expression of all the RARs (at mRNA level) in the murine models, an inverse effect was observed in human MDA-MB231 cells. ATRA (1 uM) induced an important reduction in cell number, associated with a time dependent reduction in pERK levels and an important increase in pAKT levels both in LM3 and NMuMG murine mammary cells. The same treatment on MDA-MB231 cells had no effect on cell proliferation and no modulation of MEK/ERK and PI3K/AKT pathways was observed. Moreover, ATRA treatment was associated with a reduction in PKCa and an increase in PKCd expression levels (40±14% and 60±17% respectively p<0.05 n=3) in LM3 cells, and with an increase in the expression of both PKC isoforms (3 times over control, p<0.05 n=3) in NMuMG cells. On the other side, ATRA reduced PKCa and PKCd expression levels (40±5% y 48±7% respectively p<0.05 n=3) in the MDA-MB231 human breast cancer cell line. This result indicates that the different PKC isoforms are differentially modulated by retinoids depending both of cell origin as well as tumorigenic potential. Altogether our findings support the idea of the existence of a crosstalk between retinoic and PKC systems since the activation of PKC is able to modulate the expression of retinoid receptors involved in growth and differentiation, and the treatment with ATRA modulates the expression level of different PKCs, and induced an important retardation in the growth capacity of the murine mammary cell lines. The mechanism involved the alteration of growth potential could be explained by the modulation of ATRA-non genomic signaling pathways such as MAPK/ERK and PI3K/AKT.