RNF144A is a DNA damage-induced E3 ubiquitin ligase that targets proteins involved in genome instability for degradation, e.g., DNA-PKcs and BMI1. RNF144A is frequently mutated or epigenetically silenced in cancer, providing the rationale to evaluate RNF144A loss of function in tumorigenesis. Here we report that RNF144A-deficient mice are more prone to the development of bladder tumors upon carcinogen exposure. In addition to DNA-PKcs and BMI1, we identify the immune checkpoint protein PD-L1 as a novel degradation target of RNF144A, since these proteins are expressed at higher levels in Rnf144a KO tumors. RNF144A interacts with PD-L1 in the plasma membrane and intracellular vesicles and promotes poly-ubiquitination and degradation of PD-L1. Therefore, Rnf144a KO stabilizes PD-L1 and leads to a reduction of tumor-infiltrating CD8⁺ T cell populations in the BBN-induced bladder tumors. The bladder tumors developed in WT and Rnf144a KO mice primarily express CK5 and CK14, markers of basal cancer subtype, as expected in BBN-induced bladder tumors. Intriguingly, the Rnf144a KO tumors also express GATA3, a marker for the luminal subtype, suggesting that RNF144A loss of function promotes features of cellular differentiation. Such differentiation features in Rnf144a KO tumors likely result from a decrease of EGFR expression, consistent with the reported role of RNF144A in maintaining EGFR expression. In summary, for the first time our study demonstrates the in vivo tumor suppressor activity of RNF144A upon carcinogenic insult. Loss of RNF144A promotes the expression of DNA-PKcs, BMI1 and PD-L1, likely contributing to the carcinogen-induced bladder tumorigenesis.

RNF144A 是一种 DNA 损伤诱导的 E3 泛素连接酶，可靶向参与基因组不稳定性降解的蛋白质，例如 DNA-PKcs 和 BMI1。RNF144A在癌症中经常发生突变或表观遗传沉默，为评估 RNF144A 在肿瘤发生中的功能丧失提供了依据。在这里，我们报告 RNF144A 缺陷小鼠在接触致癌物后更容易发生膀胱肿瘤。除了 DNA-PKcs 和 BMI1，我们将免疫检查点蛋白 PD-L1 确定为 RNF144A 的新降解靶标，因为这些蛋白在Rnf144a KO 肿瘤中以更高水平表达。RNF144A 与质膜和细胞内囊泡中的 PD-L1 相互作用，促进 PD-L1 的多泛素化和降解。因此，Rnf144aKO 稳定 PD-L1 并导致BBN 诱导的膀胱肿瘤中肿瘤浸润性 CD8 ^{+ T 细胞群减少。}正如在 BBN 诱导的膀胱肿瘤中所预期的那样，在 WT 和Rnf144a KO 小鼠中发育的膀胱肿瘤主要表达 CK5 和 CK14，它们是基底癌亚型的标志物。有趣的是，Rnf144a KO 肿瘤也表达 GATA3，这是一种管腔亚型的标志物，表明 RNF144A 功能丧失促进了细胞分化的特征。Rnf144a KO 肿瘤中的这种分化特征可能是由于 EGFR 表达的降低，这与 RNF144A 在维持 EGFR 表达中的报道作用一致。总之，我们的研究首次证明了体内RNF144A 在致癌损伤时的抑癌活性。RNF144A 的缺失促进了 DNA-PKcs、BMI1 和 PD-L1 的表达，可能导致致癌物诱导的膀胱肿瘤发生。