Two different unique cardiac isoforms of protein 4.1R in zebrafish, Danio rerio, and insights into their cardiac functions as related to their unique structures

FRMD4A: A potential therapeutic target for the treatment of tongue squamous cell carcinoma

The aim of the present study was to identify agents capable of inhibiting the invasion and metastasis of tongue squamous cell carcinoma and thereby improve the outcomes of patients suffering from tongue cancer. FRMD4A antibodies were used to probe 78 paraffin-embedded specimens of tongue squamous cell carcinoma and 15 normal tongue tissues, which served as controls. Immunohistochemical methods were then used for analysis. Clinical pathological parameters were obtained, and the association between FRMD4A expression in the samples and the pathological parameters was analyzed. The human tongue cancer cell line CAL27 was used to study the effects of FRMD4A. CAL27 cells were transfected with small-interfering RNA against FRMD4A (FRMD4A-siRNA) and the mRNA and protein levels of FMRD4A were then evaluated by RT-qPCR and western blot analysis, respectively. The proliferation and cell-cycle assays of CAL27 cells were evaluated using the CCK8 method and flow cytometry. The invasion and migration of the cells were measured using a Matrigel invasion chamber and a scratch assay, respectively. The results showed FRMD4A overexpression in tongue squamous cell carcinoma, and the positive reaction was predominately located in the cytoplasm. Tumor clinical stage and lymph node metastasis showed a statistically significant correlation with FRMD4A expression. Transient silencing of the FRMD4A gene for 24 and 48 h significantly decreased the mRNA and protein expression of FRMD4A, respctively. Silencing FRMD4A gene reduced the proliferation of CAL27 cells and led to cell cycle arrest in the G1 phase, as well as significantly suppressing the migration and invasion capacity of CAL27 cells. The findings of the present study suggest that FRMD4A expression correlates with the development of tongue squamous cell carcinoma. For this reason, FRMD4A merits further study as it may be suitable for use as a therapeutic agent in antitumor treatment regimens.

Increased expression of FERM domain-containing 4A protein is closely associated with the development of rectal cancer

The aim of the present study was to detect the expression levels of FERM domain-containing 4A (FRMD4A) in rectal cancer tissues and peripheral blood and to investigate the correlation between FRMD4A and cancer development. A total of 78 consecutive patients were enrolled in this study. Thirty healthy individuals were used as the control group. The expression of FRMD4A in rectal cancer and the corresponding normal adjacent tissues was detected by immunohistochemistry and western blotting. The expression of FRMD4A mRNA in peripheral blood was detected by reverse transcription-quantitative polymerase chain reaction. The expression of FRMD4A in rectal cancer tissues was found to be negatively correlated with the degree of differentiation, depth of invasion and Dukes' stage. A negative correlation was identified between FRMD4A and epithelial cadherin expression. The expression of FRMD4A in the peripheral blood of patients with rectal cancer was significantly increased compared with that in the control group (P<0.05). Expression of FRMD4A in the peripheral blood in the patients with lymph node metastasis was significantly increased compared with that in the patients without lymph node metastasis (P<0.05). These results indicate that the expression of FRMD4A is significantly increased in rectal cancer tissues and the peripheral blood of patients with rectal cancer, and the expression levels of FRMD4A are closely associated with differentiation, invasion of rectal cancer and Dukes' stage. In conclusion, the findings of the present study suggest that FRMD4A may be used as a target for the diagnosis and treatment of rectal cancer.

Isoforms of protein 4.1 are differentially distributed in heart muscle cells: relation of 4.1R and 4.1G to components of the Ca2+ homeostasis system

The 4.1 proteins are cytoskeletal adaptor proteins that are linked to the control of mechanical stability of certain membranes and to the cellular accumulation and cell surface display of diverse transmembrane proteins. One of the four mammalian 4.1 proteins, 4.1R (80 kDa/120 kDa isoforms), has recently been shown to be required for the normal operation of several ion transporters in the heart (Stagg MA et al. Circ Res, 2008; 103: 855-863). The other three (4.1G, 4.1N and 4.1B) are largely uncharacterised in the heart. Here, we use specific antibodies to characterise their expression, distribution and novel activities in the left ventricle. We detected 4.1R, 4.1G and 4.1N by immunofluorescence and immunoblotting, but not 4.1B. Only one splice variant of 4.1N and 4.1G was seen whereas there are several forms of 4.1R. 4.1N, like 4.1R, was present in intercalated discs, but unlike 4.1R, it was not localised at the lateral plasma membrane. Both 4.1R and 4.1N were in internal structures that, at the level of resolution of the light microscope, were close to the Z-disc (possibly T-tubules). 4.1G was also in intracellular structures, some of which were coincident with sarcoplasmic reticulum. 4.1G existed in an immunoprecipitable complex with spectrin and SERCA2. 80 kDa 4.1R was present in subcellular fractions enriched in intercalated discs, in a complex resistant to solubilization under non-denaturing conditions. At the intercalated disc 4.1R does not colocalise with the adherens junction protein, β-catenin, but does overlap with the other plasma membrane signalling proteins, the Na/K-ATPase and the Na/Ca exchanger NCX1. We conclude that isoforms of 4.1 proteins are differentially compartmentalised in the heart, and that they form specific complexes with proteins central to cardiomyocyte Ca(2+) metabolism.

Insights into the Function of the Unstructured N-Terminal Domain of Proteins 4.1R and 4.1G in Erythropoiesis

Membrane skeletal protein 4.1R is the prototypical member of a family of four highly paralogous proteins that include 4.1G, 4.1N, and 4.1B. Two isoforms of 4.1R (4.1R(135) and 4.1R(80)), as well as 4.1G, are expressed in erythroblasts during terminal differentiation, but only 4.1R(80) is present in mature erythrocytes. One goal in the field is to better understand the complex regulation of cell type and isoform-specific expression of 4.1 proteins. To start answering these questions, we are studying in depth the important functions of 4.1 proteins in the organization and function of the membrane skeleton in erythrocytes. We have previously reported that the binding profiles of 4.1R(80) and 4.1R(135) to membrane proteins and calmodulin are very different despite the similar structure of the membrane-binding domain of 4.1G and 4.1R(135). We have accumulated evidence for those differences being caused by the N-terminal 209 amino acids headpiece region (HP). Interestingly, the HP region is an unstructured domain. Here we present an overview of the differences and similarities between 4.1 isoforms and paralogs. We also discuss the biological significance of unstructured domains.