U20 is responsible for human herpesvirus 6B inhibition of tumor necrosis factor receptor-dependent signaling and apoptosis.

The immune system targets virus-infected cells by different means. One of the essential antiviral mechanisms is apoptosis induced by ligation of tumor necrosis factor receptor 1 (TNFR1). This receptor can be activated by tumor necrosis factor alpha (TNF-α), which upon binding to TNFR1 induces the assembly of first an inflammatory and later a proapoptotic signaling complex. Here, we report that infection by human herpesvirus 6B (HHV-6B) inhibited poly(ADP-ribose) polymerase (PARP) cleavage, caspase 3 and 8 activation, and IκBα Ser-32 phosphorylation downstream of TNFR1, indicating inhibition of both the inflammatory and apoptotic signaling pathways. We identified a hitherto uncharacterized viral protein, U20, as sufficient for mediating this inhibition. U20 was shown to locate to the cell membrane, and overexpression inhibited PARP cleavage, caspase 3 and 8 activation, IκBα Ser-32 phosphorylation, and NF-κB transcriptional activity. Moreover, small interfering RNA (siRNA) knockdown of U20 demonstrated that the protein is necessary for HHV-6B-mediated inhibition of TNFR signaling during infection. These results suggest an important novel function of U20 as a viral immune evasion protein during HHV-6B infection.

Birt-Hogg-Dubé syndrome: a case report and a review of the literature.

Background: Birt-Hogg-Dubé syndrome (BHDS) is a rare autosomal dominant inherited syndrome caused by mutations in the folliculin coding gene (FLCN). The clinical manifestations of the syndrome involve the skin, lungs, and kidneys. Because of the rarity of the syndrome, guidelines for diagnosis and management of the patients with BHDS are lacking. Objective: To present a case story and a review of the literature on BHDS in order to give an update on genetics, clinical manifestations, diagnosis, treatment, prognosis and follow-up strategies. Design: Literature review and case story. Results: A PubMed and Embase search identified 330 papers. BHDS is characterized by small benign tumors in the skin, spontaneous pneumothoraces caused by cysts in the lungs and a seven-fold increased risk of renal cancer. A case story of a young female patient presenting with pneumothorax and a family history of recurrent pneumothoraces in many relatives illustrates how the history and the diagnostic work up resulted in a diagnosis of BHDS. Conclusion: BHDS is a rare inherited disorder. In patients with spontaneous pneumothorax or cystic lung disease without any obvious explanation, BHDS should be considered. Concomitant skin manifestations, a family history of familiar pneumothorax, renal cancers and skin manifestations supports the suspicion of BHDS. Early diagnosis is important in order to subject patients to systematic screening for renal cancers. A radiological surveillance strategy for renal cancer is proposed.