Role of Autophagy in HIV-1 Matrix Protein p17-Driven Lymphangiogenesis

Abstract

AIDS-related lymphomas (ARLs) are expected to increase in the future since combined antiretroviral therapy (cART) enhances the life expectancy of HIV-1-infected (HIV ϩ ) patients but does not affect the occurrence of ARLs to the same extent as that of other tumors. Lymphangiogenesis is essential in supporting growth and metastatic spreading of ARLs. HIV-1 does not infect the neoplastic B cells, but HIV-1 proteins have been hypothesized to play a key role in sustaining a prolymphangiogenic microenvironment in lymphoid organs. The HIV-1 matrix protein p17 is detected in blood and accumulates in the germinal centers of lymph nodes of HIV ϩ patients under successful cART. The viral protein displays potent lymphangiogenic activity in vitro and in vivo. This is, at least in part, mediated by the secretion of the lymphangiogenic factor endothelin-1, suggesting that activation of a secretory pathway sustains the lymphangiogenic activity of p17. Here, we show that the p17 lymphangiogenic activity occurs on human lymph node-derived lymphatic endothelial cells (LN-LECs) under stress conditions only and relies entirely on activation of an autophagy-based pathway. In fact, induction of autophagy by p17 promotes lymphangiogenesis, whereas pharmacological and genetic inhibition of autophagy inhibits p17-triggered lymphangiogenesis. Similarly, the vasculogenic activity of p17 was totally inhibited in autophagy-incompetent mice. Our findings reveal a previously unrecognized role of autophagy in lymphangiogenesis and open the way to identify novel treatment strategies aimed at inhibiting aberrant tumordriven lymphangiogenesis in HIV ϩ patients.IMPORTANCE AIDS-related lymphomas (ARLs) are the most common malignancies in HIV-1-infected (HIV ϩ ) patients after the introduction of combined antiretroviral therapy (cART). Lymphangiogenesis is of critical importance in sustaining growth and metastasis of ARLs. Indeed, enhanced lymphangiogenesis occurs in the lymph nodes of HIV ϩ patients under successful cART. The HIV-1 matrix protein p17 is detected in blood and accumulates in the lymph node germinal centers even in the absence of virus replication. Several findings suggest a key role for p17 as a microenvironmental factor capable of promoting lymphangiogenesis. Here, we show that p17 promotes lymphangiogenesis of human lymph node-derived lymphatic endothelial cells (LN-LECs). The lymphangiogenic activity of p17 is sustained by an autophagy-based pathway that enables LN-LECs to release prolymphangiogenic factors into the extracellular microenvironment. Our findings indicate that specific targeting of autophagy may provide an important new tool for treating ARLs.KEYWORDS HIV-1 matrix protein p17, autophagy, lymphatic endothelial cells, lymphangiogenesis, AIDS-related lymphoma

Role of Autophagy in Von Willebrand Factor Secretion by Endothelial Cells and in the In Vivo Thrombin-Antithrombin Complex Formation Promoted by the HIV-1 Matrix Protein p17

“…At the same time, Beclin-1 deficient mice were completely unsensitive to the pro-coagulant p17 activity, suggesting that in vivo thrombin formation following p17 injection depends on an intact autophagy pathway. Notably, we have previously demonstrated the role of autophagy in p17-driven ET-1 secretion and angiogenesis [33]. Similarly, impaired granular exocytosis has been observed after inhibition of autophagy within different cells [5,49,50].…”

“…Interestingly, we demonstrated that angiogenesis induced by p17 is partly supported by the release of ET-1 and by activation of the ET-1/ET-1 B receptor axis [32]. ET-1 secretion from ECs upon p17 stimulation was found to rely on mechanisms of conventional secretory pathways regulated by autophagy both in vitro and in vivo [33].…”

“…In addition to the well-known mechanism of vWF secretion, which is dependent on the classical endoplasmic reticulum (ER)-Golgi complex pathway, autophagy plays a critical role in the biology of WPBs and regulates the in vitro and in vivo release of vWF [13]. Recently, p17-mediated lymphangiogenesis was found to depend on secretory autophagy pathway and secretion of ET-1 by ECs [32,33]. Thus, we tested the ability of p17 to promote vWF storage and secretion from endothelium and the involvement of autophagy in its activity.…”

“…Purified endotoxin-free recombinant p17 (from clone BH10 of clade B isolate), p24 and GST were produced as previously described [33]. The p17-neutralizing mAb MBS-3 [29] was produced in our laboratory.…”

Characterization and epitope mapping of a panel of monoclonal antibodies against HIV‐1 matrix protein

“…It was reported that the HIV‐1 infected cells can release significant amounts of virion‐free p17, which may abnormally activate host T lymphocytes and dendritic cells, induce monocyte‐mediated inflammatory, and then is associated with AIDS pathogenesis . Moreover, p17 was found to exhibit lymphangiogenesis activity in the HIV‐1 patients . Reciprocally, anti‐p17 antibodies circulating in HIV patients can suppress or retard the AIDS progression .…”