RESUMO
As confusion mounts over RNA isoforms involved in phenotypic plasticity, aberrant CpG methylation-mediated disruption of alternative splicing is increasingly recognized as a driver of intratumor heterogeneity (ITH). Protease serine 3 (PRSS3), possessing four splice variants (PRSS3-SVs; PRSS3-V1-V4), is an indispensable trypsin that shows paradoxical effects on cancer development. Here, we found that PRSS3 transcripts and their isoforms were divergently expressed in lung cancer, exhibiting opposing functions and clinical outcomes, namely, oncogenic PRSS3-V1 and PRSS3-V2 versus tumor-suppressive PRSS3-V3, by targeting different downstream genes. We identified an intragenic CpG island (iCpGI) in PRSS3. Hypermethylation of iCpGI was mediated by UHRF1/DNMT1 complex interference with the binding of myeloid zinc finger 1 (MZF1) to regulate PRSS3 transcription. The garlic-derived compound diallyl trisulfide cooperated with 5-aza-2'-deoxycytidine to exert antitumor effects in lung adenocarcinoma cells through site-specific iCpGI demethylation specifically allowing MZF1 to upregulate PRSS3-V3 expression. Epigenetic silencing of PRSS3-V3 via iCpGI methylation (iCpGIm) in BALF and tumor tissues was associated with early clinical progression in patients with lung cancer but not in those with squamous cell carcinoma or inflammatory disease. Thus, UHRF1/DNMT1-MZF1 axis-modulated site-specific iCpGIm regulates divergent expression of PRSS3-SVs, conferring nongenetic functional ITH, with implications for early detection of lung cancer and targeted therapies.
RESUMO
TMPRSS3 (transmembrane protease, serine 3) is a member of Ⅱ transmembrane serine proteases (TTSPs), and like the other members of this family, it contains typical domains including a serine protease domain, a transmembrane domain, a LDL receptor-like domain (LDLRA), and a scavenger receptor cysteine-rich domain (SRCR). Four alternative protein isoforms have been described, and isoform A is thought to be primary isoform which is expressed in many tissues, especially in the cochlea. TMPRSS3 protein is primarily localized in the endoplasmic reticulum membranes where it may be anchored by its transmembrane domain. TMPRSS3 is mutated in non-syndromic autosomal recessive deafness (DFNB8/10). Therefore TMPRSS3 is thought to be involved in the development and maintenance of the inner ear, and isoform D may be proposed as a novel diagnostic marker in ovarian carcinoma. TMPRSS3 protein is the first protease which mutation could lead to deafness. These data indicate that important signaling pathways in the inner ear are controlled by proteolytic cleavage. However, it is not clear about TMPRSS3 substrates and its function. The epithelial amiloride-sensitive sodium channel (ENaC) which is regulated by membrane-bound channel activating serine proteases (CAPs), a member of TTSPs, may be a potential substrate of TMPRSS3, but this hypothesis is still to be verified in vivo. With the development of protease research and the application of protease proteomics, substrate degradomes of a protease may therefore represent an important tool for the research of TMPRSS3 function and its molecular mechanism.