Enhanced mesenchymal stem cell survival induced by GATA-4 overexpression is partially mediated by regulation of the miR-15 family

We reported previously that pre-programming mesenchymal stem cells with the GATA-4 gene increases significantly cell survival in an ischemic environment. In this study, we tested whether regulation of microRNAs and their target proteins was associated with the cytoprotective effects of GATA-4.Methods and resultsMesenchymal stem cells were harvested from adult rat bone marrow and transduced with GATA-4 (MSC^GATA-4) using the murine stem cell virus retroviral expression system. Cells transfected with empty vector (MSC^Null) were used as controls. Quantitative real-time PCR data showed that the expression levels of miR-15 family members (miR-15b, miR-16, and miR-195) were significantly down-regulated in MSC^GATA-4. The protein expression of Bcl-w (Bcl-2-like-2), an anti-apoptotic Bcl-2 family protein, was increased in MSC^GATA-4. Hypoxic culture (low glucose and low oxygen) induced the release of lactate dehydrogenase from mesenchymal stem cells and reduced cell survival. Compared to MSC^Null, MSC^GATA-4 showed less lactate dehydrogenase release and greater cell survival following 72 h hypoxia exposure. The mitochondrial membrane potential, detected with the dye JC-1, was well maintained, and mitochondrial membrane permeability, expressed as caspase 3 and 7 activities in response to the ischemic environment was lower in MSC^GATA-4. Moreover, transfection with miR-195 significantly down-regulated Bcl-w expression in mesenchymal stem cells through a binding site in the 3′-UTR of the Bcl-w mRNA and reduced mesenchymal stem cell resistance to ischemic injury.ConclusionsThe overexpression of GATA-4 in mesenchymal stem cells down-regulates miR-15 family members, causing increased resistance to ischemia through the up-regulation of anti-apoptotic proteins in the Bcl-2 family.     

A cellulose synthase-like protein involved in hyphal tip growth and morphological differentiation in streptomyces

Cellulose synthase and cellulose synthase-like proteins, responsible for synthesizing beta-glucan-containing polysaccharides, play a fundamental role in cellular architectures, such as plant cell and tissue morphogenesis, bacterial biofilm formation, and fruiting-body development. However, the roles of the proteins involved in the developmental process are not well understood. Here, we report that a cellulose synthase-like protein (CslA(Sc)) in Streptomyces has a function in hyphal tip growth and morphological differentiation. The cslA(Sc) replacement mutant showed pleiotropic defects, including the severe delay of aerial-hyphal formation and altered cell wall morphology. Calcofluor white fluorescence analysis demonstrated that polysaccharide synthesis at hyphal tips was dependent on CslA(Sc). cslA(Sc) was constitutively transcribed, and an enhanced green fluorescent protein-CslA(Sc) fusion protein was mostly located at the hyphal tips. An extract enriched in morphogenetic chaplin proteins promoted formation of aerial hyphae by the mutant. Furthermore, a two-hybrid experiment indicated that the glycosyltransferase domain of CslA(Sc) interacted with the tropomyosin-like polarity-determining DivIVA protein, suggesting that the tip-located DivIVA governed tip recruitment of the CslA(Sc) membrane protein. These results imply that the cellulose synthase-like protein couples extracellular and cytoskeletal components functioning in tip growth and cell development.     

Improved production of the tallysomycin H-1 in Streptoalloteichus hindustanus SB8005 strain by fermentation optimization

Tallysomycin (TLM) H-1, a novel TLM analog, is the major product isolated from Streptoalloteichus hindustanus SB8005, a genetically engineered strain from S. hindustanus E465-94 ATCC 31158. Based on the structural comparison and experimental assays, TLM H-1 represents a novel bleomycin (BLM) analog displaying DNA cleavage activity similar to its parent compounds TLM and BLM, both representatives of the glycopeptide anticancer antibiotics. The low titer of TLM H-1 in the engineered SB8005 strain has greatly limited its further study. In this paper, fermentation optimization for TLM H-1 production in the SB8005 strain is described; single-factor optimization and response surface methodology proved invaluable. The results indicated that three variables including distiller’s grains and solubles, copper sulfate, and maltose out of eight parameters could significantly influence the TLM H-1 production. With systematic comparison and evaluation, the final optimized fermentation medium was determined. The optimized yield of TLM H-1 in the bench-top fermentor was 249.9 mg/L, which is 26.8 times higher than reported using the original medium, and 12.9-fold higher than that of the parent compound TLM produced by the wild-type strain. This work provides important parameters for TLM H-1 production by fermentation and should facilitate further mechanistic studies and clinical developments of TLM H-1 as an anticancer agent.