The transcription factors Junb and Fosl2 cooperate to regulate Cdh3 expression in 15P-1 Sertoli cells

A crucial stem cell plasticity regulation pathway: identification of key elements using the NCCIT human embryonic carcinoma cell line

Upon removal of stemness factors, a small subpopulation of embryonic stem cells (ESCs) spontaneously extrudes the t-SNARE protein syntaxin-4, which upregulates the cell adhesion molecule P-cadherin and induces the onset of epithelial-mesenchymal transition (EMT)-like behaviors with loss of stemness in each cell. In this study, we identified a series of molecular elements responsible for this phenomenon using several small-molecule inhibitors and the human embryonic carcinoma cell line, NCCIT. We found that the syntaxin-4-triggered morphological changes and a decrease in stemness signatures were independently induced by the activation of Rho-associated kinase (ROCK) and the abrogation of PI3K/Akt signaling. We also found that the extracellular expression of syntaxin-4 inactivated focal adhesion kinase (FAK) in association with the augmented expression of P-cadherin, and comparable controls of either of these downstream elements of syntaxin-4 accelerated both ROCK-induced F-actin stress fiber formation and P13K/Akt-suppressed loss of stemness signatures. Cells expressing P-cadherin inactivated FAK but FAK inhibition did not affect P-cadherin expression, demonstrating a causal relationship between P-cadherin and FAK in the event of syntaxin-4 induction. These results reveal a novel signaling axis in stem cells and shed new light on the crucial elements for stem cell plasticity and the maintenance of stemness.

Classical cadherins in the testis: how are they regulated?

Cadherins (CDH) are crucial intercellular adhesion molecules, contributing to morphogenesis and creating tissue barriers by regulating cells' movement, clustering and differentiation. In the testis, classical cadherins such as CDH1, CDH2 and CDH3 are critical to gonadogenesis by promoting the migration and the subsequent clustering of primordial germ cells with somatic cells. While CDH2 is present in both Sertoli and germ cells in rodents, CDH1 is primarily detected in undifferentiated spermatogonia. As for CDH3, its expression is mainly found in germ and pre-Sertoli cells in developing gonads until the establishment of the blood-testis barrier (BTB). This barrier is made of Sertoli cells forming intercellular junctional complexes. The restructuring of the BTB allows the movement of early spermatocytes toward the apical compartment as they differentiate during a process called spermatogenesis. CDH2 is among many junctional proteins participating in this process and is regulated by several pathways. While cytokines promote the disassembly of the BTB by enhancing junctional protein endocytosis for degradation, testosterone facilitates the assembly of the BTB by increasing the recycling of endocytosed junctional proteins. Mitogen-activated protein kinases (MAPKs) are also mediators of the BTB kinetics in many chemically induced damages in the testis. In addition to regulating Sertoli cell functions, follicle stimulating hormone can also regulate the expression of CDH2. In this review, we discuss the current knowledge on regulatory mechanisms of cadherin localisation and expression in the testis.

Regulation of Cdh2 by the AP-1 family transcription factor Junb in TM4 Sertoli cells

Cadherins are transmembrane proteins that mediate cell-to-cell adhesion and various cellular processes. In Sertoli cells of the testis, Cdh2 contributes to the development of the testis and the formation of the blood-testis barrier, being essential for germ cells' protection. Analyses of chromatin accessibility and epigenetic marks in adult mouse testis have shown that the region from -800 to +900 bp respective to Cdh2 transcription start site (TSS) is likely the active regulatory region of this gene. In addition, the JASPAR 2022 matrix has predicted an AP-1 binding element at about -600 bp. Transcription factors of the activator protein 1 (AP-1) family have been implicated in the regulation of the expression of genes encoding cell-to-cell interaction proteins such as Gja1, Nectin2 and Cdh3. To test the potential regulation of Cdh2 by members of the AP-1 family, siRNAs were transfected into TM4 Sertoli cells. The knockdown of Junb led to a decrease in Cdh2 expression. ChIP-qPCR and luciferase reporter assays with site-directed mutagenesis confirmed the recruitment of Junb to several AP-1 regulatory elements in the proximal region of the Cdh2 promoter in TM4 cells. Further investigation with luciferase reporter assays showed that other AP-1 members can also activate the Cdh2 promoter albeit to a lesser extent than Junb. Taken together, these data suggest that in TM4 Sertoli cells, Junb is responsible for the regulation of Cdh2 expression which requires its recruitment to the proximal region of the Cdh2 promoter.