Abstract
An occludin-focal adhesion kinase protein complex at the blood-testis barrier: A study using the cadmium model
Siu,Erica R.; Wong,Elissa W.P.; Mruk,Dolores D.; Sze,K.L.; Porto,Catarina S.; Cheng,Chuen-yan
Endocrinology 150(7): 3336-3344
Publication date: 2009
Several integral membrane proteins that constitute the blood-testisbarrier (BTB) in mammalian testes, in particular rodents, areknown to date. These include tight junction (TJ) proteins [e.g.,occludin, junctional adhesion molecule-A (JAM-A), claudins],basal ectoplasmic specialization (basal ES) proteins (e.g.,N-cadherin), and gap junction (GJ) proteins (e.g., connexin43).However, the regulators (e.g., protein kinases and phosphatases)that affect these proteins, such as their interaction with thecytoskeletal actin, which in turn confer cell adhesion at theTJ, remain largely unknown. We report herein that focal adhesionkinase (FAK) is a putative interacting partner of occludin,but not claudin-11 or JAM-A. Immunohistochemistry and fluorescentmicroscopy studies illustrated that the expression of FAK inthe seminiferous epithelium of adult rat testes was stage-specific.FAK co-localized with occludin at the BTB in virtually all stagesof the seminiferous epithelial cycle but considerably diminishedin stages VIII-IX, at the time of BTB restructuring to facilitatethe transit of primary leptotene spermatocytes. Using Sertolicells cultured in vitro with established TJ-permeability barrierand ultrastructures of TJ, basal ES and desmosome-like junctionthat mimicked the BTB in vivo, FAK was shown to co-localizewith occludin and ZO-1 at the Sertoli-Sertoli cell interface.When these Sertoli cell cultures were treated with CdCl toperturb the TJ-barrier function, occludin underwent endocytic-mediatedinternalization in parallel with FAK and ZO-1. These findingsthus demonstrate FAK is an integrated regulatory component ofthe occludin-ZO-1 protein complex, suggesting functional studiescan be performed to study the role of FAK in BTB dynamics.
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