Poly r(C) binding protein (PCBP) 1 expression is regulated by the E3 ligase UBE4A in thyroid carcinoma

Abstract

Thyroid cancer patients with high miR-490-3p inhibit translation of PCBP1 mRNA, whereas in patients with low miR-490-3p PCBP1 mRNA expression is high; however, the resultant protein is targeted for degradation through the proteasome. The objective of the present study was to evaluate the molecular mechanism that regulates post-translation degradation of poly r(C) binding protein (PCBP) 1 expression in thyroid cancer cells. Mass spectrometric analysis of PCBP1 immunoprecipitates from MG-132 treated TPC1 cells revealed a list of ubiquitin ligases associated with PCBP1. RNAi-mediated silencing of the candidate ubiquitin ligases revealed that knockdown of the ubiquitin ligase UBE4A stabilized PCBP1 in TPC1 cells. Concurrent overexpression of the candidate ubiquitin ligases in the normal thyroid epithelial cell line Nthy-ori 3-1 confirmed that ubiquitin conjugation factor E4 A (UBE4A) is the ubiquitin ligase that is degrading PCBP1. Coimmunoprecipitation of HA-tagged PCBP1 in TPC1 cells cotransfected with FLAG–UBE4A revealed robust polyubiquitinated smear of PCBP1, thus confirming UBE4A as the ubiquitin ligase of PCBP1. UBE4A expression mimicked PCBP1 mRNA expression in thyroid cancer patients and was inversely correlated to PCBP1 protein expression. Low UBE4A expression level was associated with a better prognosis in thyroid cancer patients. Our data reveal a post-translational regulatory mechanism of regulating PCBP1 expression in thyroid cancer cells.

PCBP1 depletion promotes tumorigenesis through attenuation of p27Kip1 mRNA stability and translation

“…Loss of PCBP1 is involved in various carcinogenesis [ 6 , 13 , 25 , 26 ]. Recently, PCBP1 has been shown as a negative regulator of thyroid carcinoma [ 44 ], a negative regulator of EMT related to metastasis in NSCLC [ 45 ], while PCBP1 expression is suppressed in peritoneal gastric cancer metastasis [ 46 ]. PCBP1 also can sensitize colorectal cancer to anti-cancer drug [ 47 ].…”

Multilevel regulation and molecular mechanism of poly (rC)‐binding protein 1 in cancer

“…For instance, E3 ubiquitin ligase UBE4A induced ubiquitination and degradation of PCBP1 in thyroid cancer, thereby decreasing the expression of PCBP1 protein. 16 TGF-β treatment in prostate cancer cells did not reduced the mRNA level of PCBP1, but it decreased the protein level of PCBP1 through inducing the poly-ubiquitination and degradation of PCBP1, thus resulting in the abnormal alternative splicing of CD44 and increasing the EMT. 17 In recent years, researchers have attempted to elucidate the multiple regulation of PCBP1 in tumorigenesis, development or metastasis, but the research about precise molecular mechanism was not very thorough.…”

“…65 Further research demonstrated that E3 ligase UBE4A was involved in the post-translation degradation of PCBP1 in thyroid cancer. 16 Of note, the expression of PCBP1 was significantly higher in non-small cell lung cancer tissues without lymph nodes metastasis compared with the tissues with lymph nodes metastasis. It might be correlated with TNM staging, lymph node metastasis (P < .001), and EMT-related proteins E-cadherin or vimentin.…”

“…This phenomenon may be related to the post‐translational modification of PCBP1. For instance, E3 ubiquitin ligase UBE4A induced ubiquitination and degradation of PCBP1 in thyroid cancer, thereby decreasing the expression of PCBP1 protein 16 . TGF‐β treatment in prostate cancer cells did not reduced the mRNA level of PCBP1, but it decreased the protein level of PCBP1 through inducing the poly‐ubiquitination and degradation of PCBP1, thus resulting in the abnormal alternative splicing of CD44 and increasing the EMT 17 …”

TGF-beta signaling in cancer: post-transcriptional regulation of EMT via hnRNP E1

“…Under folate deficient conditions, hnRNP E1 translationally up-regulates this transcript leading to an increase of cell surface folate receptors which promotes folate up-take [69,70]. Numerous studies have linked hnRNP E1 to the process of tumorigenesis and metastasis, demonstrating that hnRNP E1 acts as a tumor suppressor in several cancer types [5,7,8,71,72]. Silencing of hnRNP E1 results in the transition of cells to a mesenchymal phenotype, an increase in cell motility and invasiveness, and the promotion of tumor formation and distant metastases [5,6,8].…”