The extracellular matrix component laminin promotes gap junction formation in the rat anterior pituitary gland

Abstract

Folliculo-stellate (FS) cells in the anterior pituitary gland are believed to have multifunctional properties. FS cells connect to each other not only by mechanical means, but also by gap junctional cell-to-cell communication. Using transgenic rats that express green fluorescent protein (GFP) specifically in FS cells in the anterior pituitary gland (S100b-GFP rats), we recently revealed that FS cells in primary culture markedly change their shape, and form numerous interconnections with neighboring FS cells in the presence of laminin, an extracellular matrix (ECM) component of the basement membrane. Morphological and functional changes in cells are believed to be partly modified by matricrine signaling, by which ECM components function as cellular signals. In the present study, we examined whether gap junction formation between FS cells is affected by matricrine cues. A cell sorter was used to isolate FS cells from male S100b-GFP rat anterior pituitary for primary culture. We observed that mRNA and protein levels of connexin 43 in gap junction channels were clearly higher in the presence of laminin. In addition, we confirmed the formation of gap junctions between FS cells in primary culture by electron microscopy. Interestingly, we also observed that FS cells in the presence of laminin displayed well-developed rough endoplasmic reticulum and Golgi apparatus. Our findings suggest that, in anterior pituitary gland, FS cells may facilitate functional roles such as gap junctional cell-to-cell communication by matricrine signaling.

Matrix metalloproteinase-9 expression in folliculostellate cells of rat anterior pituitary gland

“…The present study showed that MMP-9 inhibition suppressed proliferative activity of FS cells on laminin, which indicates that MMP-9 is necessary in FS cell division (Figs 3G and 4D). Proliferation of FS cells on laminin involves integrin b1, which is associated with caveolin-3, and uses MAPK signal transduction, which upregulates the cyclin D1 expression that drives the cell cycle (Horiguchi et al 2011b). Despite the marked decrease in BrdU incorporation after MMP-9 silencing, cyclin D1 expression was unchanged in this study (Fig.…”

“…With respect to these ligand specificities, we recently reported that FS cells bind laminin through integrin-a3b1 and/or integrin-a6b1 (Horiguchi et al 2010). Since laminin induces integrin b1 signaling in FS cells (Horiguchi et al 2011b), we hypothesize that the increase in MMP-9 expression in the presence of laminin occurs via a similar pathway. Furthermore, the increases in MMP-9 mRNA expression and protein (in cell lysate and secreted into medium) in the presence of laminin parallel the phenotypic change in FS cell shape from round to stellate .…”

Expression of the proteoglycan syndecan-4 and the mechanism by which it mediates stress fiber formation in folliculostellate cells in the rat anterior pituitary gland

“…Knowledge of the topographic features of FS cells is essential in understanding these lobular structures, the location of FS cells in the core of the lobular structure, and the characteristic envelopment of hormone-producing cells by their cytoplasmic processes, the tips of which attach to the ECM (Soji & Herbert 1989, Inoue et al 1999, Shirasawa et al 2004. In our studies on FS cell activity in the presence of ECM (Horiguchi et al 2010(Horiguchi et al , 2011a, we have shown that FS cells markedly extend their cytoplasmic processes and form networks at gap junctions. In this study, we have shown that FS cells under the influence of laminin extend their cytoplasmic processes due to a syndecan-4-dependent mechanism that leads to activation of a-actinin in FS cells.…”

“…Furthermore, we showed that FS cells in the presence of ECM markedly prolong their cytoplasmic processes, form numerous interconnections with neighboring FS cells, and promote assembly of the FS cell network (Horiguchi et al 2010(Horiguchi et al , 2011a. However, it is not clear how FS cells under the influence of ECM prolong their cytoplasmic processes and initiate network construction with other FS cells in primary culture.…”

“…Total RNA fractions were prepared, and cDNA was synthesized as described previously (Horiguchi et al 2011a). Quantitative real-time PCR (ABI PRISM 7900HT; Applied Biosystems) was performed by using gene-specific primers and SYBR Premix Ex Taq (Takara, Tokyo, Japan) containing SYBR Green I.…”