ABSTRACT
RNA sequencing of untreated and r-Moj-DM treated SK-Mel-28 cells was performed after 6 h, to begin unraveling the apoptotic pathway induced by r-Moj-DM. Bioinformatic analyses of RNA sequencing data yielded 40 genes that were differentially expressed. Nine genes were upregulated and 31 were downregulated. qRT-PCR was used to validate differential expression of 13 genes with known survival or apoptotic-inducing activities. Expression of BNiP3, IGFBP3, PTPSF, Prune 2, TGF-ß, and TXNIP were compared from cells treated with r-Moj-DN (a strong apoptotic inducer) or r-Moj-DA (a non-apoptotic inducer) for 1 h, 2 h, 4 h, and 6 h after treatment. Our results demonstrate that significant differences in expression are only detected after 4 h of treatment. In addition, expression of TXNIP (an apoptotic inducer) remains elevated at 4 h and 6 h only in r-Moj-DN treated cells. Based on the consistency of elevated TXNIP expression, we further studied TXNIP as a novel target of disintegrin activation. Confocal microscopy of anti-TXNIP stained SK-Mel-28 cells suggests nuclear localization of TXNIP after r-Moj-DM treatment. A stable TXNIP knockdown SK-Mel-28 cell line was produced to test TXNIP' role in the apoptotic induction by r-Moj-DM. High cell viability (74.3% ±9.1) was obtained after r-Moj-DM treatment of TXNIP knocked down SK-Mel-28 cells, compared to 34% ±0.187 for untransduced cells. These results suggest that TXNIP is required early in the apoptotic-inducing pathway resulting from r-Moj-DM binding to the αv integrin subunit.
Subject(s)
Apoptosis/drug effects , Carrier Proteins/physiology , Disintegrins/toxicity , Sequence Analysis, RNA , Apoptosis/physiology , Carrier Proteins/genetics , Cell Line , Gene Knockdown Techniques , HumansABSTRACT
Disintegrins are small peptides produced in viper venom that act as integrin antagonists. When bound to integrins, disintegrins induce altered cellular behaviors, such as apoptotic induction. Disintegrins with RGDDL or RGDDM motifs induce apoptosis of normal and cancer cells. We hypothesized that a second aspartate (D) carboxyl to the RGD is sufficient to induce apoptosis. Five recombinant mojastin D mutants were produced by site-directed mutagenesis (r-Moj-DA, r-Moj-DG, r-Moj-DL, r-Moj-DN, and r-Moj-DV). Stable αv integrin knockdown and shRNA scrambled control SK-Mel-28 cell lines were produced to test a second hypothesis: r-Moj-D_ peptides bind to αv integrin. Only r-Moj-DL, r-Moj-DM, and r-Moj-DN induced apoptosis of SK-Mel-28 cells (at 29.4%, 25.6%, and 36.2%, respectively). Apoptotic induction was significantly reduced in SK-Mel-28 cells with a stable αv integrin knockdown (to 2%, 17%, and 2%, respectively), but not in SK-Mel-28 cells with a stable scrambled shRNA. All six r-Moj-D_ peptides inhibited cell proliferation; ranging from 49.56% (r-Moj-DN) to 75.6% (r-Moj-DA). Cell proliferation inhibition by r-Moj-D_ peptides was significantly reduced in SK-Mel-28 cells with a stable αv integrin knockdown. All six r-Moj-D_ peptides inhibited SK-Mel-28 cell migration at high levels (69%-100%). As a consequence, rac-1 mRNA expression levels were significantly reduced as early as 1 h after treatment, suggesting that rac-1 is involved in the cell migration activity of SK-Mel-28.
