ITM2A

Abstract: The PKA-CREB signaling pathway is involved in many cellular processes including autophagy. Recent studies demonstrated that PKA-CREB inhibits autophagy in yeast; however, the role of PKA-CREB signaling in mammalian cell autophagy has not been fully characterized. Here, we report that the integral membrane protein ITM2A expression is positively regulated by PKA-CREB signaling and ITM2A expression interferes with autophagic flux by interacting with vacuolar ATPase (v-ATPase). The ITM2A promoter contains a CRE element, and mutation at the CRE consensus site decreases the promoter activity. Forskolin treatment and PKA expression activate the ITM2A promoter confirming that ITM2A expression is dependent on the PKA-CREB pathway. ITM2A expression results in the accumulation of autophagosomes and interferes with autolysosome formation by blocking autophagic flux. We demonstrated that ITM2A physically interacts with v-ATPase and inhibits lysosomal function. These results support the notion that PKA-CREB signaling pathway regulates ITM2A expression, which negatively regulates autophagic flux by interfering with the function of v-ATPase.

Abstract: Itm2A is a novel type II integral membrane protein that is involved in osteo- and chondrogenic differentiation. Itm2a cDNA was originally isolated from a cDNA library of organ cultures from prenatal mouse mandibular condyles, by subtractive hybridization and differential screening. The Itm2a gene was isolated from a BALB/c liver genomic library. In total, 9.4 kb of the gene were sequenced, of which 2649 bp are 5′ flanking sequences. The Itm2a gene contains six exons and five introns. The splice sites conform to the GT/AG rule. The 5′ flanking region, which contains the presumed promoter sequence, lacks the common TATAA and CCAAT sequences, but contains consensus binding sites for various transcription factors. Several of these transcription factors are known to play a role in transcriptional regulation of cartilage- or bone-specific genes (e.g. Cbfa1, Cart-1, MHox, HES-1, and CIIS1). Itm2a was mapped to mouse chromosome position XA2-XA3 by fluorescent in situ hybridization (FISH) analysis. The human homolog, ITM2A, was mapped to chromosome position Xq13.3-Xq21.2.