The ErbB3-binding protein EBP1 modulates lapatinib sensitivity in prostate cancer cells

PA2G4 in health and disease: An underestimated multifunctional regulator

BACKGROUND

Proliferation-associated protein 2G4 (PA2G4), also known as ErbB3-binding protein 1 (EBP1), is an evolutionarily conserved, ubiquitously expressed, multifunctional factor in health and disease. In recent decades, its role as a sophisticated regulator in a broad range of biological processes has drawn widespread attention from researchers.

AIM OF REVIEW

We introduce the molecular structure, functional modules, and post-translational modifications of PA2G4. We further elaborate on its role and function in immune microenvironment modulation, cell growth, neural homeostasis and embryonic development. In particular, we summarize its relevance to tumorigenesis and cancer progression and describe its molecular mechanisms in regulating the hallmarks of cancers. This review aims to provide a comprehensive blueprint of PA2G4 functions and to inspire further basic and translational studies.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Owing to its versatile domains and motifs, PA2G4 regulates a variety of molecular processes, including transcription, translation, proteostasis and epigenetic modulation, suggesting its critical roles in maintaining homeostasis. There are two isoforms of the PA2G4 protein: PA2G4-p42 and PA2G4-p48. While both isoforms regulate cellular activities, they often exert distinct or even contradictory effects. Dysfunction and aberrant expression of PA2G4 isoforms lead to the occurrence and progression of various diseases, indicating their role as predictive markers or therapeutic targets.

GNL3 and PA2G4 as Prognostic Biomarkers in Prostate Cancer

Prostate cancer is a multifocal and heterogeneous disease common in males and remains the fifth leading cause of cancer-related deaths worldwide. The prognosis of prostate cancer is variable and based on the degree of cancer and its stage at the time of diagnosis. Existing biomarkers for the prognosis of prostate cancer are unreliable and lacks specificity and sensitivity in guiding clinical decision. There is need to search for novel biomarkers having prognostic and predictive capabilities in guiding clinical outcomes. Using a bioinformatics approach, we predicted GNL3 and PA2G4 as biomarkers of prognostic significance in prostate cancer. A progressive increase in the expression of GNL3 and PA2G4 was observed during cancer progression having significant association with poor survival in prostate cancer patients. The Receiver Operating Characteristics of both genes showed improved area under the curve against sensitivity versus specificity in the pooled samples from three different GSE datasets. Overall, our analysis predicted GNL3 and PA2G4 as prognostic biomarkers of clinical significance in prostate cancer.

HER2-intronic miR-4728-5p facilitates HER2 expression and accelerates cell proliferation and migration by targeting EBP1 in breast cancer

HER2 amplification greatly contributes to the tumorigenesis of multiple cancers. Intronic miR-4728-5p is transcribed along with its host gene HER2. However, little is known about the role of miR-4728-5p in cancer. This study aims to elucidate the potential role of miR-4728-5p and the underlying mechanism in breast cancer. Kaplan-Meier analysis showed that higher expression of HER2 led to worse survival outcomes in breast cancer patients. The TCGA dataset revealed that compared to normal breast tissues, HER2 and miR-4728-5p levels were significantly upregulated in breast cancer tissues with a positive correlation. In functional assays, miR-4728-5p was confirmed to promote the proliferation and migration in breast cancer cell BT474. EBP1 was identified as a direct target of miR-4728-5p via bioinformatics and luciferase reporter assays. miR-4728-5p was further demonstrated to increase HER2 expression and promote cell proliferation and migration by directly inhibiting EBP1 in breast cancer. Taken together, the HER2-intronic miR-4728-5p/EBP1/HER2 feedback loop plays an important role in promoting breast cancer cell proliferation and migration. Our study provides novel insights for targeted therapies of breast cancer.

ERRF sensitizes ERBB2-positive breast cancer cells to lapatinib treatment likely by attenuating MCL1 and ERBB2 expression

Previously we found that the estrogen receptor (ER) related factor ERRF regulates cell proliferation and tumor growth, and its expression is positively associated with ER status and better survival but inversely associated with ERBB2 (also named HER2) status in breast cancer. Here we report that ERRF also plays an important role in the response of ERBB2-positive breast cancer cells to lapatinib, a dual tyrosine kinase inhibitor that interrupts the ERBB2 and EGFR pathway. In ERBB2-positive breast cancer cell lines, lower levels of ERRF expression correlated with lapatinib resistance, restoration of ERRF expression in lapatinib-resistant cell lines JIMT-1 and MDA-MB-453 enhanced their lapatinib responses, and knockdown of ERRF in lapatinib sensitive cell lines BT-474 and SK-BR-3 caused lapatinib resistance. ERRF-enhanced lapatinib sensitivity was also confirmed in xenograft tumors of JIMT-1 cells. In patients with ERBB2-positive breast cancer, higher level of ERRF expression correlated with both pathologic complete response (pCR) to lapatinib and better survival. Mechanistically, ERRF expression in resistant cells promoted lapatinib-induced apoptosis by attenuating MCL1 and ERBB2 expression. These results suggest that ERRF plays an important role in lapatinib response of ERBB2-positive breast cancer, and further study of ERRF could lead to improved prediction and sensitivity of lapatinib response.