Fibroblast growth factors regulate prolactin transcription via an atypical Rac-dependent signaling pathway

PKCα and PKCδ: Friends and Rivals

PKC comprises a large family of serine/threonine kinases that share a requirement for allosteric activation by lipids. While PKC isoforms have significant homology, functional divergence is evident among subfamilies and between individual PKC isoforms within a subfamily. Here, we highlight these differences by comparing the regulation and function of representative PKC isoforms from the conventional (PKCα) and novel (PKCδ) subfamilies. We discuss how unique structural features of PKCα and PKCδ underlie differences in activation and highlight the similar, divergent, and even opposing biological functions of these kinases. We also consider how PKCα and PKCδ can contribute to pathophysiological conditions and discuss challenges to targeting these kinases therapeutically.

The anterior pituitary gap junctions: potential targets for toxicants

The anterior pituitary regulates endocrine organs and physiological activities in the body. Environmental pollutants and drugs deleterious to the endocrine system may affect anterior pituitary activity through direct action on anterior pituitary cells. Within the gland, endocrine and folliculostellate cells are organized into and function as individual tridimensional networks, each network regulating its activity by coordinating the connected cells' responses to physiological or pathological cues. The gap junctions connecting endocrine cells and/or folliculostellate cells allow transmission of information among cells that is necessary for adequate network function. Toxicants may affect gap junctions as well as the physiology of the anterior pituitary. However, whether toxicants effects on anterior pituitary hormone secretion involve gap junctions is unknown. The folliculostellate cell gap junctions are sensitive to hormones, cytokines and growth factors. These cells may be an interesting experimental model for evaluating whether toxicants target anterior pituitary gap junctions.

Systematic analysis of copy number variants of a large cohort of orofacial cleft patients identifies candidate genes for orofacial clefts

Orofacial clefts (OFCs) represent a large fraction of human birth defects and are one of the most common phenotypes affected by large copy number variants (CNVs). Due to the limited number of CNV patients in individual centers, CNV analyses of a large number of OFC patients are challenging. The present study analyzed 249 genomic deletions and 226 duplications from a cohort of 312 OFC patients reported in two publicly accessible databases of chromosome imbalance and phenotype in humans, DECIPHER and ECARUCA. Genomic regions deleted or duplicated in multiple patients were identified, and genes in these overlapping CNVs were prioritized based on the number of genes encompassed by the region and gene expression in embryonic mouse palate. Our analyses of these overlapping CNVs identified two genes known to be causative for human OFCs, SATB2 and MEIS2, and 12 genes (DGCR6, FGF2, FRZB, LETM1, MAPK3, SPRY1, THBS1, TSHZ1, TTC28, TULP4, WHSC1, WHSC2) that are associated with OFC or orofacial development. Additionally, we report 34 deleted and 24 duplicated genes that have not previously been associated with OFCs but are associated with the BMP, MAPK and RAC1 pathways. Statistical analyses show that the high number of overlapping CNVs is not due to random occurrence. The identified genes are not located in highly variable genomic regions in healthy populations and are significantly enriched for genes that are involved in orofacial development. In summary, we report a CNV analysis pipeline of a large cohort of OFC patients and identify novel candidate OFC genes.

Biphasic Effect of Basic Fibroblast Growth Factor on Anterior Pituitary Folliculostellate TtT/GF Cell Coupling, and Connexin 43 Expression and Phosphorylation

Basic fibroblast growth factor (bFGF) is a mitogenic and differentiating cytokine. In the anterior pituitary, folliculostellate (FS) cells constitute the major source of bFGF. bFGF affects endocrine cell proliferation and secretion in the anterior pituitary. In addition, bFGF increases its own expression by acting directly on FS cells. FS cell Cx43-mediated gap junction intercellular communication allows the establishment of an intrapituitary network for the transmission of information. In the present study, we assessed how bFGF regulates FS cell coupling. Time course studies were carried out on the FS cell line TtT/GF. Short-term bFGF treatment induced a transient cell uncoupling and the phosphorylation in Ser368 of membrane-bound Cx43 without modifying Cx43 levels. We demonstrated the involvement of the protein kinase C (PKC) isoform α in the phosphorylation of Cx43 in S368. Moreover, we showed that bFGF induced PKCα activation by stimulating its expression, phosphorylation and association with the plasma membrane. The long-term incubation with bFGF increased TtT/GF cell coupling, total Cx43 levels and Cx43 accumulation at the cell membrane of cytoplasmic projections. The Cx43 level increase was a result of the stimulation of Cx43 gene transcription as mediated by the extracellular-regulated kinase 1/2 signalling pathway. Taken together, the data show that bFGF modulates TtT/GF cell coupling by activating different pathways that lead to opposite effects on Cx43 phosphorylation and expression depending on the duration of the exposure of the cells to bFGF. A short-term bFGF exposure reduces cell-to-cell communication as a mean of desynchronising FS cells. By contrast, long-term exposure to bFGF enhances cell-to-cell communication and facilitates coordination among FS cells.

Key signaling molecules in pituitary tumors

In pituitary tumorigenesis there is cross-talk between fine deregulation of intracellular pathways and complex microenvironmental factors, processes that can be modulated at various levels. The signaling pathways of growth, angiogenic factors and hormones are intricate; therefore, alterations induced upon node-molecules can lead to aberrant proliferation. The demonstrated overactivity of AKT and MAPK pathways qualifies them as valuable targets for inhibition mediated by somatostatin analogues. An increasing body of evidence suggests clinically significant implications of PTTG1 in correlation with aggressive phenotypes or survival rate, thus PTTG1 is an interesting candidate biomarker for malignancy, tumor staging and subsequent therapeutic interventions. Future work should focus on understanding the molecular mechanisms that control pituitary tumor transformation, where intracellular signaling molecules will constitute not only diagnostic/prognostic markers but also novel therapeutic targets.

Prospective of Ras signaling in stem cells

The Ras signaling pathway plays a predominant role during development and controls diverse biological process in all eukaryotic cells. It is a member of the large family of GTPases proteins that binds and hydrolyzes GTP. Ras is a lipid-anchored protein on the intracellular membrane compartments, and cycles between inactive GDP-bound and the signaling competent GTP-bound conformation. Studies have demonstrated Ras to be a central regulator in signal transduction pathways responding to diverse extracellular and intracellular stimuli. Much progress has been made towards delineating specific genes involved in the process of pluripotency and differentiation of stem cells. Here, we discuss recent aspects of Ras signaling pathways in mediating stem cell properties.

Rac/Rho pathway regulates actin depolymerization induced by aminoglycoside antibiotics

Stress stimuli can lead to remodeling of the actin cytoskeleton and subsequent alteration of cell adhesion and permeation as well as cell functions and cell fate. We investigated redox-dependent Rho GTPase-linked pathways controlling the actin cytoskeleton in the inner ear of the CBA mouse, by using aminoglycoside antibiotics as a noxious stimulus that causes loss of sensory cells via the formation of reactive oxygen species. Kanamycin treatment in vivo interfered with the formation of F-actin, disturbed the arrangement of beta-actin in the stereocilia of outer hair cells, and altered the intermittent adherens junction/tight junction complexes between outer hair cells and supporting cells. The drug treatment also activated Rac1 and promoted the formation of the complex of Rac1 and p67phox while decreasing the activity of RhoA and reducing the formation of the RhoA/p140mDia complex. In inner-ear-derived cell lines, expression of mutated Rac1 changed the structural arrangement of F-actin and diminished the immunoreactivity of p140mDia. These findings suggest that actin depolymerization induced by kanamycin is mediated by Rac1 activation, followed by the formation of superoxide by NADPH oxidase. These changes will ultimately contribute to aminoglycoside-induced loss of hair cells.

Fibroblast growth factor-2 and epidermal growth factor modulate prolactin responses to TRH and dopamine in primary cultures

Fibroblast growth factor-2 (FGF-2) and epidermal growth factor (EGF) are expressed in most tissues of the organism including pituitary. FGF-2 increases PRL levels and PRL mRNA in GH3 cells and primary cultures, and it has been involved in the lactotroph proliferation and hyperplasia. EGF also increases PRL levels in vitro. However, the effects of these two factors in the responses of lactotroph cells to TRH and dopamine (DA) remain to be clarified. In the present work we have studied the modulator activity of FGF-2 and EGF on in vitro PRL in responses to TRH and DA in primary cultures from in vivo vehicle- or estrogen (E2)-treated rats. We have found that FGF-2 (2 x 10(-11) M) prevents the EGF-induced dose-dependent increase in PRL levels in control cells, and reversed the EGF-stimulating effects in cells from E2-treated rats. Both FGF-2 (2 x 10(-11) M) and EGF (6.6 x 10(-9) M) significantly increase (>30% and >120%, respectively) the PRL levels in response to TRH (10(-6), 10(-5) M). FGF-2 blocked the inhibitory effects of low doses of DA (10(-9) M). EGF was unable to do so, although markedly increased (>200%) the post-DA PRL rebound. In cells from in vivo E2-treated rats, FGF-2 increased (>50%) the PRL secretion in response to TRH, while EGF reduced responses to high doses of TRH (10(-6), 10(-5) M). In addition, FGF-2 reversed and EGF increased the inhibitory effects of DA. Both FGF-2 and EGF completely blocked the post-DA PRL rebound, in these cells. Taken together our data suggest that FGF-2 and EGF are important regulators of lactotroph responsiveness to TRH and DA in vitro, although their actions are highly dependent on estrogenic milieu.

Differential regulation of cell growth and gene expression by FGF-2 and FGF-4 in pituitary lactotroph GH4 cells

Fibroblast growth factors, FGF-2 and FGF-4, are reported to play divergent roles in pituitary differentiation and tumor formation, stimulating cell differentiation or proliferation, respectively. However, mitogenic responses to FGFs have not been extensively characterized and little is known about the molecular mechanisms by which specific FGF isoforms may mediate distinct biological responses. Here we show that FGF-4 but not FGF-2 stimulated DNA synthesis and cell proliferation in GH4 cells. Microarray analyses revealed that FGF-4 induced expression of several oncogenes, growth factor receptors and cell cycle control proteins (e.g. cyclin D3/cdk4, N-myc, c-Raf, insulin and thyroid hormone receptors) while FGF-2 had no effect or down regulated these same genes. These transcriptional responses are consistent with a proliferative and/or tumorigenic role for FGF-4 versus a growth inhibitory effect of FGF-2. FGF-2 and FGF-4 also differentially regulated MAP kinase phosphorylation, which may underlie their isoform-specific effects on cell growth and gene expression.

Tumor necrosis factor-alpha activates the human prolactin gene promoter via nuclear factor-kappaB signaling

Pituitary function has been shown to be regulated by an increasing number of intrapituitary factors, including cytokines. Here we show that the important cytokine TNF-alpha activates prolactin gene transcription in pituitary GH3 cells stably expressing luciferase under control of 5 kb of the human prolactin promoter. Similar regulation of the endogenous rat prolactin gene by TNF-alpha in GH3 cells was confirmed using real-time PCR. Luminescence microscopy revealed heterogeneous dynamic response patterns of promoter activity in individual cells. In GH3 cells treated with TNF-alpha, Western blot analysis showed rapid inhibitory protein kappaB (IkappaBalpha) degradation and phosphorylation of p65. Confocal microscopy of cells expressing fluorescence-labeled p65 and IkappaBalpha fusion proteins showed transient cytoplasmic-nuclear translocation and subsequent oscillations in p65 localization and confirmed IkappaBalpha degradation. This was associated with increased nuclear factor kappaB (NF-kappaB)-mediated transcription from an NF-kappaB-responsive luciferase reporter construct. Disruption of NF-kappaB signaling by expression of dominant-negative variants of IkappaB kinases or truncated IkappaBalpha abolished TNF-alpha activation of the prolactin promoter, suggesting that this effect was mediated by NF-kappaB. TNF-alpha signaling was found to interact with other endocrine signals to regulate prolactin gene expression and is likely to be a major paracrine modulator of lactotroph function.

Multifaceted role of Rho proteins in angiogenesis

The Rho family of GTPases is part of the Ras superfamily. The Rho, Rac, and Cdc42 members of the family are present in mammalian cells and have been the subject of attention of researchers due to their vast spectrum of functions. Rac 1, Cdc42, and RhoA are well-known for their role in the regulation of the actin cytoskeleton in promoting the formation of lamellipodia, filopodia, and stress fibers, respectively. The Rho proteins also participate in the control of cell growth, motility, cell-cell adhesions, morphogenesis, cytoskeletal dynamics, and cellular trafficking. The mechanisms for eliciting these functions have become clearer during the last decade. Concordant with their roles in multiple processes of cellular control, the Rho proteins have been shown to be involved in tumor growth, progression, metastasis, and now angiogenesis.