ABSTRACT
The inflammatory repressor TNIP1/ABIN-1 is important for keeping in check inflammatory and cell-death pathways to avoid potentially dangerous sustained activation of these pathways. We have now found that TNIP1 is rapidly degraded by selective macroautophagy/autophagy early (0-4 h) after activation of TLR3 by poly(I:C)-treatment to allow expression of pro-inflammatory genes and proteins. A few hours later (6 h), TNIP1 levels rise again to counteract sustained inflammatory signaling. TBK1-mediated phosphorylation of a TNIP1 LIR motif regulates selective autophagy of TNIP1 by stimulating interaction with Atg8-family proteins. This is a novel level of regulation of TNIP1, whose protein level is crucial for controlling inflammatory signaling.
Subject(s)
Autophagy , DNA-Binding Proteins , Microtubule-Associated Proteins , Humans , Amino Acid Motifs , Autophagy/physiology , Autophagy-Related Protein 8 Family/metabolism , Microtubule-Associated Proteins/metabolism , Phosphorylation , Transcription Factors/metabolism , DNA-Binding Proteins/metabolismABSTRACT
Intercellular communication via gap junctions has an important role in controlling cell growth and in maintaining tissue homeostasis. Connexin 43 (Cx43; also known as GJA1) is the most abundantly expressed gap junction channel protein in humans and acts as a tumor suppressor in multiple tissue types. Cx43 is often dysregulated at the post-translational level during cancer development, resulting in loss of gap junctions. However, the molecular basis underlying the aberrant regulation of Cx43 in cancer cells has remained elusive. Here, we demonstrate that the oncogenic E3 ubiquitin ligase NEDD4 regulates the Cx43 protein level in HeLa cells, both under basal conditions and in response to protein kinase C activation. Furthermore, overexpression of NEDD4, but not a catalytically inactive form of NEDD4, was found to result in nearly complete loss of gap junctions and increased lysosomal degradation of Cx43 in both HeLa and C33A cervical carcinoma cells. Collectively, the data provide new insights into the molecular basis underlying the regulation of gap junction size and represent the first evidence that an oncogenic E3 ubiquitin ligase promotes loss of gap junctions and Cx43 degradation in human carcinoma cells.
