Regulators of G protein signaling (RGS) are a family of proteins that attenuate the activity of the trimeric G proteins. RGS proteins act as GTPase-activating proteins (GAPs) for the ␣ subunits of several trimeric G proteins, much like the GAPs that regulate the activity of monomeric G proteins such as Ras. RGS proteins have been cloned from many eukaryotes, and those whose biochemical activity has been characterized regulate the members of the G i family of G proteins; some forms can also act on G q proteins. In an ongoing effort to elucidate the role of G z ␣ in cell signaling, the yeast twohybrid system was employed to identify proteins that could interact with a mutationally activated form of G z ␣. A novel RGS, termed RGSZ1, was identified that is most closely related to two existing RGS proteins termed RetRGS1 and GAIP. Northern blot analysis revealed that expression of RGSZ1 was limited to brain, and expression was particularly high in the caudate nucleus. Biochemical characterization of recombinant RGSZ1 protein revealed that RGSZ1 was indeed a GAP and, most significantly, showed a marked preference for G z ␣ over other members of the G i ␣ family. Phosphorylation of G z ␣ by protein kinase C, an event known to occur in cells and that was previously shown to influence ␣-␤␥ interactions of G z , rendered the G protein much less susceptible to RGSZ1 action.

G z is a member of the G i family of trimeric G proteins whose primary role in cell physiology is still unknown. In an ongoing effort to elucidate the cellular functions of G z , the yeast two-hybrid system was employed to identify proteins that specifically interact with a mutationally activated form of G␣ z . One of the molecules uncovered in this screen was Rap1GAP, a previously identified protein that specifically stimulates GTP hydrolytic activity of the monomeric G protein Rap1 and thus is believed to function as a down-regulator of Rap1 signaling. Like G z , the precise role of Rap1 in cell physiology is poorly understood. Biochemical analysis using purified recombinant proteins revealed that the physical interaction between G␣ z and Rap1GAP blocks the ability of RGSs (regulators of G protein signaling) to stimulate GTP hydrolysis of the ␣ subunit, and also attenuates the ability of activated G␣ z to inhibit adenylyl cyclase. Structure-function analyses indicate that the first 74 amino-terminal residues of Rap1GAP, a region distinct from the catalytic core domain responsible for the GAP activity toward Rap1, is required for this interaction. Co-precipitation assays revealed that G␣ z , Rap1GAP, and Rap1 can form a stable complex. These data suggest that Rap1GAP acts as a signal integrator to somehow coordinate and/or integrate G z signaling and Rap1 signaling in cells.

To promote preventive care-seeking, these results affirm the importance of interventions that promote discrimination-free environments for gender minorities.

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Pre-exposure prophylaxis (PrEP) has the potential to be an empowering HIV prevention tool among female sex workers (FSW), yet little is known about PrEP awareness and interest in this population. Sex workers and Police Promoting Health in Risky Environments (SAPPHIRE) is a prospective cohort study of street-based FSW in Baltimore, MD. A cross-sectional analysis explored awareness and interest in PrEP among HIV-negative FSW. Multivariable Poisson regressions modeled associations between individual, interpersonal, and structural variables and PrEP awareness and interest. Of n = 232 FSW, 66% were white, half were less than 35 years old, 59% injected drugs daily, and 66% sold sex daily. Only 21% of FSW were aware of PrEP, though 74% were interested. PrEP awareness was associated with experiencing client condom coercion [adjusted incidence rate ratio (aIRR) = 0.50, 95% CI: 0.28-0.90] and condomless sex with an intimate partner (aIRR = 0.54, 95% CI: 0.30-0.98). PrEP interest was associated with perceiving PrEP as ''very easy'' to take (aIRR = 1.91, 95% CI: 1.49-2.45) and moving to an unfamiliar geographic area to sell sex (aIRR = 1.20, 95% CI: 1.04-1.39). Women who had a current gonorrhea or chlamydia infection were less likely to be interested in PrEP (aIRR = 0.75, 95% CI: 0.59-0.95). Though PrEP awareness among FSW is low, there are FSW who are significantly more likely to express interest in PrEP and outreach efforts should target these women. Results suggest that women-controlled HIV prevention methods may be important for reducing incidence among FSW.

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G z is a member of the family of trimeric guanine nucleotide-binding regulatory proteins (G proteins), which plays a crucial role in signaling across cell membranes. The expression of G z is predominately confined to neuronal cells and platelets, suggesting an involvement in a neuroendocrine process. Although the signaling pathway in which G z participates is not yet known, it has been linked to inhibition of adenylyl cyclase. We have found that arachidonate and related unsaturated fatty acids suppress guanine nucleotide binding to the ␣ subunit of G z . This inhibition of nucleotide binding by cisunsaturated fatty acids is specific for G z␣ ; other G protein ␣ subunits are relatively insensitive to these lipids. The IC 50 for inhibition by the lipids closely corresponds to their critical micellar concentrations, suggesting that the interaction of the lipid micelle with G z␣ is the primary event leading to inhibition. The presence of the acidic group of the fatty acid is critical for inhibition, as no effect is observed with the corresponding fatty alcohol. While arachidonic acid produces near-complete inhibition of both GDP and guanosine 5-(3-O-thio)triphosphate binding by G z␣ , release of GDP from the protein was unaffected. Furthermore, the rate of inactivation of G z␣ by arachidonate is essentially identical to the rate of GDP release from the protein, indicating that GDP release is required for inactivation. These observations indicate that the mechanism of inactivation of G z␣ by unsaturated fatty acids is through an interaction of an acidic lipid micelle with the nucleotide-free form of the protein. Although the physiologic significance of this finding is unclear, similar effects of unsaturated fatty acids on other proteins involved in cell signaling indicate potential roles for these lipids in signal modulation. Additionally, the ability of arachidonate to inactivate this adenylyl cyclase-inhibitory G protein provides a molecular mechanism for previous findings that treatment of platelets with arachidonate results in elevated cAMP levels.

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