Dottorato di Ricerca in Cellular Biochemistry and drug activity in oncology, Ciclo XXIII, a.a. 2009-2010In the search for new cancer chemo-preventive compounds, hundreds of naturally
occurring molecules have been evaluated. Among these, antioxidants appear to be
very promising. In this contest, over the last decade retinoids, natural and synthetic
substances structurally related to vitamin A, are often used as part of a combined
therapy and have been object of intense investigation. However, clinical trials have
shown that retinoids can also be deleterious and are associated with the activation of
proto-oncogenes, leading to an increased incidence of neoplasias. In fact, retinoic
acid (RA) partition is regulated by cognate intracellular lipid binding proteins
(iLBPs): cellular retinoic acid binding protein II (CRABP-II) delivers RA to RARs,
while fatty acid binding protein 5 (FABP5) shuttles the RA to PPARβ/δ. In cells with
high CRABP-II/FABP5 ratio, RA functions through RAR acting as a pro-apoptotic
agent, while signaling through PPARβ/δ promotes survival in those cells highly
expressing FABP5. So that, in some tissues RA promotes cell survival and
hyperplasia. The apparently conflicting data regarding the pro-oxidant/ anti-oxidant
and proliferative/anti-proliferative potential of different retinoids molecules,
stimulated us to investigate the effect of RA on cell proliferation and its mechanisms
in two different tumor Leydig cell lines (MLTC-1 and R2C) using as normal phenotype counterpart the Leydig TM-3 cell line. Our previous data demonstrated
how pharmacological doses of RA induce cell death via the apoptotic pathway in
Leydic TM-3 cell line. Recently dose-response treatment of TM-3, MLTC-1 and R2C
with RA at nutraceutic/physiological doses, promotes cell proliferation accompanied
by stimulation of antioxidant enzymes activity (CAT, GST), decreases p21 levels and
fosters cell cycle progression via activation of the IP3K/Akt pathway in the cancer
cell line, while administration of pharmacological doses of RA still results in
apoptosis. Interestingly treatment with 500 nM of RA resulted in cytosolic
vacuolization, hallmark of the autophagic process. Autophagy is a major cellular
pathway for the degradation of long-lived proteins and organelles in eukaryotic cells.
A large number of intracellular/extracellular stimuli, including amino acid starvation,
testosterone production and invasion of microorganisms are able to induce
autophagic response. In addition, retinoic acid is also implicated in a post-translation
modification called retinoylation that modify, in vitro, the activity of the
mitochondrial carrier oxo-chetoglutarate (OCG).
Moreover, retinoids are often used as part of a combined therapy, their action is
prevalently mediated by two types of receptor RAR and RXR. This latter, is also
called master coordinator due to its versatility to heterodimering with several nuclear
receptor. Thus, we have elucidated the molecular mechanism by which combined treatment with rosiglitazone (BRL) and 9 cis retinoic acid (9cRA) at nanomolar doses
triggers apoptotic events in breast cancer cells, suggesting potential therapeutic uses
for these compounds, demonstrating an up-regulation of tumor suppressor gene p53
and its activity is due to the NFkB site, giving emphasis to the potential use of the
combined therapy with low doses of both BRL and 9cRA as novel therapeutic tool
particularly for breast cancer patients who develop resistance to anti-estrogen
therapy. Recently, 9cRA was found as endogenous in pancreas highlighted its rule in
both glucose stimulated insulin secretion (GSIS) mechanism and glucose
homeostasis, establishing it as autocoid hormone with a unique physiological
function among retinoids, and broaden insight into mechanisms of GSISUniversity of Calabri
