Vitamin D inhibits human immunodeficiency virus type 1 and Mycobacterium tuberculosis infection in macrophages through the induction of autophagy

The cellular autophagy pathway modulates human T-cell leukemia virus type 1 replication

Autophagy, a general homeostatic process for degradation of cytosolic proteins or organelles, has been reported to modulate the replication of many viruses. The role of autophagy in human T-cell leukemia virus type 1 (HTLV-1) replication has, however, been uncharacterized. Here, we report that HTLV-1 infection increases the accumulation of autophagosomes and that this accumulation increases HTLV-1 production. We found that the HTLV-1 Tax protein increases cellular autophagosome accumulation by acting to block the fusion of autophagosomes to lysosomes, preventing the degradation of the former by the latter. Interestingly, the inhibition of cellular autophagosome-lysosome fusion using bafilomycin A increased the stability of the Tax protein, suggesting that cellular degradation of Tax occurs in part through autophagy. Our current findings indicate that by interrupting the cell's autophagic process, Tax exerts a positive feedback on its own stability.

Toll-like receptor 8 ligands activate a vitamin D mediated autophagic response that inhibits human immunodeficiency virus type 1

Toll-like receptors (TLR) are important in recognizing microbial pathogens and triggering host innate immune responses, including autophagy, and in the mediation of immune activation during human immunodeficiency virus type-1 (HIV) infection. We report here that TLR8 activation in human macrophages induces the expression of the human cathelicidin microbial peptide (CAMP), the vitamin D receptor (VDR) and cytochrome P450, family 27, subfamily B, polypeptide 1 (CYP27B1), which 1α-hydroxylates the inactive form of vitamin D, 25-hydroxycholecalciferol, into its biologically active metabolite. Moreover, we demonstrate using RNA interference, chemical inhibitors and vitamin D deficient media that TLR8 agonists inhibit HIV through a vitamin D and CAMP dependent autophagic mechanism. These data support an important role for vitamin D in the control of HIV infection, and provide a biological explanation for the benefits of vitamin D. These findings also provide new insights into potential novel targets to prevent and treat HIV infection.

Cells use macroautophagy (autophagy - ‘self-eating’, lysosome-dependent degradation and recycling of intracellular components in response to stress) as a mechanism to detect intracellular pathogens through pattern-recognition receptors such as Toll-like receptors (TLRs) that recognize signature molecules of pathogens that are essential for their survival. One such Toll-like receptor, TLR8, which is located in human macrophage endosomes, recognizes both imidazoquinoline compounds and uridine-rich single-stranded RNA such as human immunodeficiency virus type-1 (HIV) single-stranded RNA. In the present study we report that TLR8 activation in human macrophages induces the expression of the human cathelicidin microbial peptide (CAMP), the vitamin D receptor (VDR), and cytochrome P450, family 27, subfamily B, polypeptide 1 (CYP27B1), which 1α-hydroxylates the inactive form of vitamin D, 25-hydroxycholecalciferol, into its biologically active metabolite. Moreover, we demonstrate that TLR8 activation induces autophagy in human macrophages through a vitamin D and CAMP dependent mechanism, and that the induction of autophagy by TLR8 agonists inhibits HIV. These data support an important role for vitamin D in the control of HIV infection, and provide a biological explanation for the benefits of vitamin D. These findings also provide new insights into potential novel targets to prevent and treat HIV infection.

Impact of cellular autophagy on viruses: Insights from hepatitis B virus and human retroviruses

Autophagy is a protein degradative process important for normal cellular metabolism. It is apparently used also by cells to eliminate invading pathogens. Interestingly, many pathogens have learned to subvert the cell’s autophagic process. Here, we review the interactions between viruses and cells in regards to cellular autophagy. Using findings from hepatitis B virus and human retroviruses, HIV-1 and HTLV-1, we discuss mechanisms used by viruses to usurp cellular autophagy in ways that benefit viral replication.

Autophagy modulation as a potential therapeutic target for diverse diseases

Autophagy is an essential, conserved lysosomal degradation pathway that controls the quality of the cytoplasm by eliminating protein aggregates and damaged organelles. It begins when double-membraned autophagosomes engulf portions of the cytoplasm, which is followed by fusion of these vesicles with lysosomes and degradation of the autophagic contents. In addition to its vital homeostatic role, this degradation pathway is involved in various human disorders, including metabolic conditions, neurodegenerative diseases, cancers and infectious diseases. This article provides an overview of the mechanisms and regulation of autophagy, the role of this pathway in disease and strategies for therapeutic modulation.