High molecular weight FGF2 isoforms demonstrate canonical receptor-mediated activity and support human embryonic stem cell self-renewal.

Basic fibroblast growth factor (FGF2) is a highly pleiotropic member of a large family of growth factors with a broad range of activities, including mitogenesis and angiogenesis (Ornitz et al., 1996; Zhang et al., 2006), and it is known to be essential for maintenance of balance between survival, proliferation, and self-renewal in human pluripotent stem cells (Eiselleova et al., 2009; Zoumaro-Djayoon et al., 2011). A single FGF2 transcript can be translated into five FGF2 protein isoforms, an 18kDa low molecular weight (LMW) isoform and four larger high molecular weight (HMW) isoforms (Arese et al., 1999; Arnaud et al., 1999). As they are not generally secreted, high molecular weight (HMW) FGF2 isoforms have predominantly been investigated intracellularly; only a very limited number of studies have investigated their activity as extracellular factors. Here we report over-expression, isolation, and biological activity of all recombinant human FGF2 isoforms. We show that HMW FGF2 isoforms can support self-renewal of human embryonic stem cells (hESCs) in vitro. Exogenous supplementation with HMW FGF2 isoforms also activates the canonical FGFR/MAPK pathway and induces mitogenic activity in a manner similar to that of the 18kDa FGF2 isoform. Though all HMW isoforms, when supplemented exogenously, are able to recapitulate LMW FGF2 activity to some degree, it appears that certain isoforms tend to do so more poorly, demonstrating a lesser functional response by several measures. A better understanding of isoform-specific FGF2 effects will lead to a better understanding of developmental and pathological FGF2 signaling.

Characterization of the Enzymatic Activity of SETDB1 and Its 1:1 Complex with ATF7IP.

The protein methyltransferase (PMT) SETDB1 is a strong candidate oncogene in melanoma and lung carcinomas. SETDB1 methylates lysine 9 of histone 3 (H3K9), utilizing S-adenosylmethionine (SAM) as the methyl donor and its catalytic activity, has been reported to be regulated by a partner protein ATF7IP. Here, we examine the contribution of ATF7IP to the in vitro activity and substrate specificity of SETDB1. SETDB1 and ATF7IP were co-expressed and 1:1 stoichiometric complexes were purified for comparison against SETDB1 enzyme alone. We employed both radiometric flashplate-based and SAMDI mass spectrometry assays to follow methylation on histone H3 15-mer peptides, where lysine 9 was either unmodified, monomethylated, or dimethylated. Results show that SETDB1 and the SETDB1:ATF7IP complex efficiently catalyze both monomethylation and dimethylation of H3K9 peptide substrates. The activity of the binary complex was 4-fold lower than SETDB1 alone. This difference was due to a decrease in the value of kcat as the substrate KM values were comparable between SETDB1 and the SETDB1:ATF7IP complex. H3K9 methylation by SETDB1 occurred in a distributive manner, and this too was unaffected by the presence of ATF7IP. This finding is important as H3K9 can be methylated by HMTs other than SETDB1 and a distributive mechanism would allow for interplay between multiple HMTs on H3K9. Our results indicate that ATF7IP does not directly modulate SETDB1 catalytic activity, suggesting alternate roles, such as affecting cellular localization or mediating interaction with additional binding partners.

Near-infrared photoinactivation of bacteria and fungi at physiologic temperatures.

We examined a laser system (870 and 930 nm), employing wavelengths that have exhibited cellular photodamage properties in optical traps. In vitro, with 1.5 cm diameter flat-top projections (power density of 5.66 W cm(-2)), at physiologic temperatures, we achieved photoinactivation of Staphylococcus aureus, Escherichia coli, Candida albicans and Trichophyton rubrum. Using nonlethal dosimetry, we measured a decrease in trans-membrane potentials (DeltaPsimt and DeltaPsip) and an increase in reactive oxygen species (ROS) generation in methicillin-resistant S. aureus (MRSA), C. albicans and human embryonic kidney cells. We postulate that these multiplexed wavelengths cause an optically mediated mechano-transduction of cellular redox pathways, decreasing DeltaPsi and increasing ROS. The cellular energetics of prokaryotic and fungal pathogens, along with mammalian cells, are affected in a similar manner when treated with these multiplexed wavelengths at the power densities employed. Following live porcine thermal tolerance skin experiments, we then performed human pilot studies, examining photodamage to MRSA in the nose and fungi in onychomycosis. No observable damage to the nares or the nail matrix was observed, yet photodamage to the pathogens was achieved at physiologic temperatures. The selective aspect of this near-infrared photodamage presents the possibility for its future utilization in human cutaneous antimicrobial therapy.