由先前声称的非编码RNA的非规范开放阅读框（ORF）编码的肽/小蛋白，最近被认识到具有重要的生物学功能，但大部分尚未被表征。1p36是一个重要的肿瘤抑制基因（TSG）位点，经常在多种癌症中发生缺失，其关键的TSGs如TP73，PRDM16和CHD5已被证实。我们的CpG甲基组分析确定了一个被沉默的1p36.3基因KIAA0495，之前被认为编码长非编码RNA。我们发现KIAA0495的第2个开放阅读框实际上是编码蛋白质的，并且翻译出一个小蛋白质SP0495。KIAA0495转录本在多个正常组织中广泛表达，但在多种肿瘤细胞系和原发肿瘤中，包括结肠直肠癌，食管癌和乳腺癌，经常被启动子CpG甲基化沉默。其下调/甲基化与癌症患者的生存不良有关。SP0495能够在体外和体内诱导肿瘤细胞凋亡，细胞周期停滞，衰老和自噬，同时抑制肿瘤细胞生长。在机制上，SP0495作为一个脂质结合蛋白，结合磷脂酰肌醇（PtdIns（3）P，PtdIns（3,5）P2），能够抑制AKT的磷酸化及其下游信号，进一步抑制致癌的AKT/mTOR、NF-κB和Wnt/β-catenin信号。SP0495还通过调控磷脂酰肌醇转换和自噬/蛋白酶降解，调节自噬调节因子BECN1和SQSTM1/p62的稳定性。因此，我们发现并验证了一个位于1p36.3的小蛋白SP0495，作为一个磷脂酰肌醇结合蛋白发挥作用，调节AKT信号激活和自噬，被多种肿瘤启动子甲基化失活，其可能成为潜在的生物标志物。 ©2023。作者已授权给ADMC Associazione Differenziamento e Morte Cellulare。

Peptides/small proteins, encoded by noncanonical open reading frames (ORF) of previously claimed non-coding RNAs, have recently been recognized possessing important biological functions, but largely uncharacterized. 1p36 is an important tumor suppressor gene (TSG) locus frequently deleted in multiple cancers, with critical TSGs like TP73, PRDM16, and CHD5 already validated. Our CpG methylome analysis identified a silenced 1p36.3 gene KIAA0495, previously thought coding long non-coding RNA. We found that the open reading frame 2 of KIAA0495 is actually protein-coding and translating, encoding a small protein SP0495. KIAA0495 transcript is broadly expressed in multiple normal tissues, but frequently silenced by promoter CpG methylation in multiple tumor cell lines and primary tumors including colorectal, esophageal and breast cancers. Its downregulation/methylation is associated with poor survival of cancer patients. SP0495 induces tumor cell apoptosis, cell cycle arrest, senescence and autophagy, and inhibits tumor cell growth in vitro and in vivo. Mechanistically, SP0495 binds to phosphoinositides (PtdIns(3)P, PtdIns(3,5)P2) as a lipid-binding protein, inhibits AKT phosphorylation and its downstream signaling, and further represses oncogenic AKT/mTOR, NF-κB, and Wnt/β-catenin signaling. SP0495 also regulates the stability of autophagy regulators BECN1 and SQSTM1/p62 through modulating phosphoinositides turnover and autophagic/proteasomal degradation. Thus, we discovered and validated a 1p36.3 small protein SP0495, functioning as a novel tumor suppressor regulating AKT signaling activation and autophagy as a phosphoinositide-binding protein, being frequently inactivated by promoter methylation in multiple tumors as a potential biomarker.© 2023. The Author(s), under exclusive licence to ADMC Associazione Differenziamento e Morte Cellulare.