Proteolytic Control of Lipid Metabolism.

Synthesis and regulation of lipid levels and identities is critical for a wide variety of cellular functions, including structural and morphological properties of organelles, energy storage, signaling, and stability and function of membrane proteins. Proteolytic cleavage events regulate and/or influence some of these lipid metabolic processes and as a result help modulate their pleiotropic cellular functions. Proteins involved in lipid regulation are proteolytically cleaved for the purpose of their relocalization, processing, turnover, and quality control, among others. The scope of this review includes proteolytic events governing cellular lipid dynamics. After an initial discussion of the classic example of sterol regulatory element-binding proteins, our focus will shift to the mitochondrion, where a range of proteolytic events are critical for normal mitochondrial phospholipid metabolism and enforcing quality control therein. Recently, mitochondrial phospholipid metabolic pathways have been implicated as important for the proliferative capacity of cancers. Thus, the assorted proteases that regulate, monitor, or influence the activity of proteins that are important for phospholipid metabolism represent attractive targets to be manipulated for research purposes and clinical applications.

Phosphatidylethanolamine made in the inner mitochondrial membrane is essential for yeast cytochrome bc1 complex function.

Of the four separate PE biosynthetic pathways in eukaryotes, one occurs in the mitochondrial inner membrane (IM) and is executed by phosphatidylserine decarboxylase (Psd1). Deletion of Psd1 is lethal in mice and compromises mitochondrial function. We hypothesize that this reflects inefficient import of non-mitochondrial PE into the IM. Here, we test this by re-wiring PE metabolism in yeast by re-directing Psd1 to the outer mitochondrial membrane or the endomembrane system and show that PE can cross the IMS in both directions. Nonetheless, PE synthesis in the IM is critical for cytochrome bc1 complex (III) function and mutations predicted to disrupt a conserved PE-binding site in the complex III subunit, Qcr7, impair complex III activity similar to PSD1 deletion. Collectively, these data challenge the current dogma of PE trafficking and demonstrate that PE made in the IM by Psd1 support the intrinsic functionality of complex III.

Time-Course Analysis of Gene Expression During the Saccharomyces cerevisiae Hypoxic Response.

Many cells experience hypoxia, or low oxygen, and respond by dramatically altering gene expression. In the yeast Saccharomyces cerevisiae, genes that respond are required for many oxygen-dependent cellular processes, such as respiration, biosynthesis, and redox regulation. To more fully characterize the global response to hypoxia, we exposed yeast to hypoxic conditions, extracted RNA at different times, and performed RNA sequencing (RNA-seq) analysis. Time-course statistical analysis revealed hundreds of genes that changed expression by up to 550-fold. The genes responded with varying kinetics suggesting that multiple regulatory pathways are involved. We identified most known oxygen-regulated genes and also uncovered new regulated genes. Reverse transcription-quantitative PCR (RT-qPCR) analysis confirmed that the lysine methyltransferase EFM6 and the recombinase DMC1, both conserved in humans, are indeed oxygen-responsive. Looking more broadly, oxygen-regulated genes participate in expected processes like respiration and lipid metabolism, but also in unexpected processes like amino acid and vitamin metabolism. Using principle component analysis, we discovered that the hypoxic response largely occurs during the first 2 hr and then a new steady-state expression state is achieved. Moreover, we show that the oxygen-dependent genes are not part of the previously described environmental stress response (ESR) consisting of genes that respond to diverse types of stress. While hypoxia appears to cause a transient stress, the hypoxic response is mostly characterized by a transition to a new state of gene expression. In summary, our results reveal that hypoxia causes widespread and complex changes in gene expression to prepare the cell to function with little or no oxygen.

Determinants of survival for Native American adults with HIV infection.

Few if any Native American/Alaska Native (NA/AN) people have been included in highly active antiretroviral therapy (HAART) treatment trials or epidemiologic studies, leaving little data on which to be assured of the efficacy of HAART in this unique population. This study aims to evaluate the impact of HAART and review determinants of survival in a cohort of NA/AN persons receiving treatment for HIV in a real life clinical setting. A retrospective chart review of 235 HIV-infected Native Americans receiving services at an urban medical center operated by the Indian Health Service from January 1, 1981 through June 30, 2004 was conducted, providing 782.7 person-years of follow-up. The main outcome measures were time from study entry and from incident AIDS diagnosis to death. Death rates fell from 18.4 (13.3-25.4) per 100 person-years in the period prior to 1998 to 6.4 (4.6-8.8) per 100 person-years in the years 1998-2004, (RR 0.35, p < 0.0001). Factors associated with the greatest reduction in risk of death from time of study entry were current use of HAART, HR 0.13 (0.06-0.30, p < 0.001), and CD4 count >/=200 at entry, HR 0.16 (0.08-0.35, p < 0.001). Current use of HAART was the strongest predictor of survival from time of AIDS diagnosis, HR 0.11 (0.05-0.25, p < 0.001). The use of HAART therapy and CD4 count were primary predictors of survival. Earlier diagnosis and access to effective medical treatment will be key factors in reducing disparities in health brought about by HIV infection in Native American/Alaska Native communities.