Induction of apoptosis and cell cycle arrest by Bis (2-ethylhexyl) phthalate produced by marine Bacillus pumilus MB 40

Abstract

Marine microorganisms represent a potential source for the production of biomedically useful compounds active against inflammation, cancer, diabetes, etc. Marine Bacillus pumilus MB 40 (GenBank accession no. HQ705771) isolated from deep sea water column (1000m depth) near Andaman and Nicobar islands produced a bioactive lead, Bis (2-ethylhexyl) phthalate (BEHP) with a molecular formula of C6H4(CO2C8H17)2 and a molecular ion at m/z 391 (M+). Anti proliferative effect of the isolated compound was examined by MTT assay in human erythroleukemic K562 cells and the IC50 of BEHP was found to be 21μM. BEHP was able to induce apoptosis involving caspases pathway, besides regulating mitochondrial enzymes. Further, western blot analysis revealed the activation of caspases family proteins viz., caspase 8, caspase-9 and caspase-3. An increase in the expression of Bax mRNA concomitant with a decrease in mRNA of Bcl-2 in BEHP treated K562 cells was also observed. AO/EB staining of BEHP treated K562 cells further confirmed the progression of apoptosis as evidenced by morphological changes including nuclear condensation, cell shrinkage, and formation of apoptotic bodies. Treatment of K562 cells with BEHP induced the progressive accumulation of fragmented DNA in a time dependent manner. This pattern appeared as a typical laddering distribution of DNA fragmentation due to intranucleosomal cleavage associated with apoptosis. Based on flow cytometric analysis it has become evident that the compound was also effective in arresting the cell cycle at a sub G0/G1 phase.