Novel BRCA2-Interacting Protein, LIMD1, Is Essential for the Centrosome Localization of BRCA2 in Esophageal Cancer Cell

LIMD1 phosphorylation in mitosis is required for mitotic progression and its tumor-suppressing activity

LIM domains containing 1 (LIMD1) is a member of the Zyxin family proteins and functions as a tumor suppressor in lung cancer. LIMD1 has been shown to regulate Hippo-YAP signaling activity. Here, we report a novel regulatory mechanism for LIMD1. We found that cyclin-dependent kinase 1 (CDK1) and c-Jun NH2-terminal kinases 1/2 (JNK1/2) phosphorylate LIMD1 in vitro and in cells during anti-tubulin drug-induced mitotic arrest. Phosphorylation also occurs during normal mitosis. S272, S277, S421, and S424 were identified as the main phosphorylation sites in LIMD1. Deletion of LIMD1 resulted in a shortened mitotic cell cycle and phosphorylation of LIMD1 is required for proper mitotic progression. We further showed that the phosphorylation-deficient mutant LIMD1-4A is less active in suppressing cell proliferation, anchorage-independent growth, cell migration, and invasion in lung cancer cells. Together, our findings suggest that LIMD1 is a key regulator of mitotic progression, and that dysregulation of LIMD1 contributes to tumorigenesis.

Silencing of LIMD1 promotes proliferation and reverses cell adhesion-mediated drug resistance in non-Hodgkin's lymphoma

LIM domains-containing protein 1 (LIMD1) is a tumor suppressor protein downregulated in numerous solid malignancies. However, the functional role of LIMD1 in non-Hodgkin's lymphoma (NHL) remains unclear. In the present study, it was demonstrated that LIMD1 is associated with the proliferation of NHL and cell adhesion mediated-drug resistance (CAM-DR). It was indicated by western blot analysis that LIMD1expression is lower in progressive lymphoma compared with indolent lymphoma. Furthermore, it was indicated that the role of LIMD1 in cell viability and proliferation remains unclear. Finally, the present study demonstrated that LIMD1 serves an important role in CAM-DR by regulating cell cycle progression. Silencing of LIMD1 may reverse CAM-DR in NHL. Therefore, the findings of the present study suggested that LIMD1 may be a potential therapeutic target for patients with NHL.

LIMD1 is a survival prognostic marker of gastric cancer and hinders tumor progression by suppressing activation of YAP1

Purpose

The purpose of this study was to investigate the clinical significance of LIMD1 and its biological roles in gastric cancer (GC).

Materials and methods

The prognostic value of LIMD1 in GC patients was determined by the online tool Kaplan–Meier Plotter. The biological functions of LIMD1 in GC were examined by in vitro assays, including proliferation, anchorage-independent growth, migration, invasion, and epithelial to mesenchymal transition (EMT) assays. The levels of downstream YAP1 regulated by LIMD1 were measured by Western blot analysis, and the sub-localization of YAP1 in GC cells was visualized by immunofluorescence staining. Differential expression levels and copy number levels of LIMD1 between GC and normal tissues were compared using the Oncomine database. A correlation of LIMD1 mRNA level and the copy number level was depicted by cBioPortal. We also evaluated the methylation status around the LIMD1 genes by Wanderer.

Results

The expression level of LIMD1 positively correlated with the prognosis of GC patients regardless of tumor stage, size, lymph node, metastasis, Lauren’s classification, differentiation, gender, treatment, and ERBB2 amplification status. Overexpression of LIMD1 impeded the tumor growth, cell motility, invasiveness, and metastasis, and knockdown of LIMD1 promoted these phenotypes in GC cells. Mechanistically, YAP1 was one of the downstream effectors of LIMD1; LIMD1 suppressed the expression of YAP1 as well as its intracellular translocation. Furthermore, we found that LIMD1 expression was reduced in some of the GC profiling datasets. Gene deletion, instead of DNA methylation, contributed to the reduced expression of LIMD1 in GC.

Conclusion

Our results identified LIMD1 as a convincing prognostic marker as well as a potentially therapeutic target for GC.

A HIF-LIMD1 negative feedback mechanism mitigates the pro-tumorigenic effects of hypoxia

The adaptive cellular response to low oxygen tensions is mediated by the hypoxia-inducible factors (HIFs), a family of heterodimeric transcription factors composed of HIF-α and HIF-β subunits. Prolonged HIF expression is a key contributor to cellular transformation, tumorigenesis and metastasis. As such, HIF degradation under hypoxic conditions is an essential homeostatic and tumour-suppressive mechanism. LIMD1 complexes with PHD2 and VHL in physiological oxygen levels (normoxia) to facilitate proteasomal degradation of the HIF-α subunit. Here, we identify LIMD1 as a HIF-1 target gene, which mediates a previously uncharacterised, negative regulatory feedback mechanism for hypoxic HIF-α degradation by modulating PHD2-LIMD1-VHL complex formation. Hypoxic induction of LIMD1 expression results in increased HIF-α protein degradation, inhibiting HIF-1 target gene expression, tumour growth and vascularisation. Furthermore, we report that copy number variation at the LIMD1 locus occurs in 47.1% of lung adenocarcinoma patients, correlates with enhanced expression of a HIF target gene signature and is a negative prognostic indicator. Taken together, our data open a new field of research into the aetiology, diagnosis and prognosis of LIMD1-negative lung cancers.

Differential transmission of the molecular signature of RBSP3, LIMD1 and CDC25A in basal/ parabasal versus spinous of normal epithelium during head and neck tumorigenesis: A mechanistic study

Head and neck squamous cell carcinoma (HNSCC) is a global disease and mortality burden, necessitating the elucidation of its molecular progression for effective disease management. The study aims to understand the molecular profile of three candidate cell cycle regulatory genes, RBSP3, LIMD1 and CDC25A in the basal/ parabasal versus spinous layer of normal oral epithelium and during head and neck tumorigenesis. Immunohistochemical expression and promoter methylation was used to determine the molecular signature in normal oral epithelium. The mechanism of alteration transmission of this profile during tumorigenesis was then explored through additional deletion and mutation in HPV/ tobacco etiological groups, followed byclinico-pathological correlation. In basal/parabasal layer, the molecular signature of the genes was low protein expression/ high promoter methylation of RBSP3, high expression/ low methylation of LIMD1 and high expression of CDC25A. Dysplastic epithelium maintained the signature of RBSP3 through high methylation/ additional deletion with loss of the signatures of LIMD1 and CDC25A via deletion/ additional methylation. Similarly, maintenance and / or loss of signature in invasive tumors was by recurrent deletion/ methylation. Thus, differential patterns of alteration of the genes might be pre-requisite for the development of dysplastic and invasive lesions. Etiological factors played a key role in promoting genetic alterations and determining prognosis. Tobacco negative HNSCC patients had significantly lower alterations of LIMD1 and CDC25A, along with better survival among tobacco negative/ HPV positive patients. Our data suggests the necessity for perturbation of normal molecular profile of RBSP3, LIMD1 and CDC25A in conjunction with etiological factors for head and neck tumorigenesis, implying their diagnostic and prognostic significance.