Hexavalent Chromium Targets Securin to Drive Numerical Chromosome Instability in Human Lung Cells.

Hexavalent chromium [Cr(VI)] is a known human lung carcinogen with widespread exposure in environmental and occupational settings. Despite well-known cancer risks, the molecular mechanisms of Cr(VI)-induced carcinogenesis are not well understood, but a major driver of Cr(VI) carcinogenesis is chromosome instability. Previously, we reported Cr(VI) induced numerical chromosome instability, premature centriole disengagement, centrosome amplification, premature centromere division, and spindle assembly checkpoint bypass. A key regulator of these events is securin, which acts by regulating the cleavage ability of separase. Thus, in this study we investigated securin disruption by Cr(VI) exposure. We exposed human lung cells to a particulate Cr(VI) compound, zinc chromate, for acute (24 h) and prolonged (120 h) time points. We found prolonged Cr(VI) exposure caused marked decrease in securin levels and function. After prolonged exposure at the highest concentration, securin protein levels were decreased to 15.3% of control cells, while securin mRNA quantification was 7.9% relative to control cells. Additionally, loss of securin function led to increased separase activity manifested as enhanced cleavage of separase substrates; separase, kendrin, and SCC1. These data show securin is targeted by prolonged Cr(VI) exposure in human lung cells. Thus, a new mechanistic model for Cr(VI)-induced carcinogenesis emerges with centrosome and centromere disruption as key components of numerical chromosome instability, a key driver in Cr(VI) carcinogenesis.

Studies in a Murine Model Confirm the Safety of Griffithsin and Advocate Its Further Development as a Microbicide Targeting HIV-1 and Other Enveloped Viruses.

Griffithsin (GRFT), a lectin from Griffithsia species, inhibits human immunodeficiency virus-1 (HIV-1) replication at sub-nanomolar concentrations, with limited cellular toxicity. However, in vivo safety of GRFT is not fully understood, especially following parenteral administration. We first assessed GRFT's effects in vitro, on mouse peripheral blood mononuclear cell (mPBMC) viability, mitogenicity, and activation using flow-cytometry, as well as cytokine secretion through enzyme-linked immunosorbent assay (ELISA). Toxicological properties of GRFT were determined after a single subcutaneous administration of 50 mg/kg or 14 daily doses of 10 mg/kg in BALB/c mice. In the context of microbicide development, toxicity of GRFT at 2 mg/kg was determined after subcutaneous, intravaginal, and intraperitoneal administrations, respectively. Interestingly, GRFT caused no significant cell death, mitogenicity, activation, or cytokine release in mPBMCs, validating the usefulness of a mouse model. An excellent safety profile for GRFT was obtained in vivo: no overt changes were observed in animal fitness, blood chemistry or CBC parameters. Following GRFT treatment, reversible splenomegaly was observed with activation of certain spleen B and T cells. However, spleen tissues were not pathologically altered by GRFT (either with a single high dose or chronic doses). Finally, no detectable toxicity was found after mucosal or systemic treatment with 2 mg/kg GRFT, which should be further developed as a microbicide for HIV prevention.

Investigation of griffithsin's interactions with human cells confirms its outstanding safety and efficacy profile as a microbicide candidate.

Many natural product-derived lectins such as the red algal lectin griffithsin (GRFT) have potent in vitro activity against viruses that display dense clusters of oligomannose N-linked glycans (NLG) on their surface envelope glycoproteins. However, since oligomannose NLG are also found on some host proteins it is possible that treatment with antiviral lectins may trigger undesirable side effects. For other antiviral lectins such as concanavalin A, banana lectin and cyanovirin-N (CV-N), interactions between the lectin and as yet undescribed cellular moieties have been reported to induce undesirable side effects including secretion of inflammatory cytokines and activation of host T-cells. We show that GRFT, unlike CV-N, binds the surface of human epithelial and peripheral blood mononuclear cells (PBMC) through an exclusively oligosaccharide-dependent interaction. In contrast to several other antiviral lectins however, GRFT treatment induces only minimal changes in secretion of inflammatory cytokines and chemokines by epithelial cells or human PBMC, has no measureable effect on cell viability and does not significantly upregulate markers of T-cell activation. In addition, GRFT appears to retain antiviral activity once bound to the surface of PBMC. Finally, RNA microarray studies show that, while CV-N and ConA regulate expression of a multitude of cellular genes, GRFT treatment effects only minimal alterations in the gene expression profile of a human ectocervical cell line. These studies indicate that GRFT has an outstanding safety profile with little evidence of induced toxicity, T-cell activation or deleterious immunological consequence, unique attributes for a natural product-derived lectin.