Progress 07/01/00 to 01/31/05
Outputs
Prolactinomas are tumors of the prolactin-secreting lactotropes in the pituitary gland and are the most frequently occurring neoplasms in the human pituitary. In the general population, 1 in 2800 men and 1 in 1050 women have prolactinomas. Patients with prolactinomas typically show elevated levels of plasma prolactin (hyperprolactinemia). Prolactinoma development has been linked to estrogen exposure in both humans and animals. We have provided evidence that estradiol acts directly on lactotropes to increase prolactin secretion, whereas estradiol increases cell proliferation by altering cell-to-cell communication between pituitary cells. We have previously shown that under estrdiol influence, lactotropes secrete transforming growth factor beta 3 (TGF-beta3), which increases the release of basic fibroblast growth factor (bFGF) from FS cells to control lactotropic cell proliferation in the pituitary gland. Our recent studies identified the cellular mechanism by which bFGF
increases cell proliferation. We studied the role of mitogen-activated protein (MAP) kinase p44/42 in bFGF-regulated cell proliferation using enriched lactotropes and the lactotrope-derived PR1 cell line. In cell cultures, bFGF increased cell proliferation of PR1 cells and enriched lactotropes. In both of these cell populations, bFGF also increased phosphorylation of MAP kinase p44/42. U0126, an inhibitor of MAP kinase p44/42, blocked the bFGF-induced activation of MAP kinase p44/42 as well as the bFGF-induced cell proliferation of enriched lactotropes and PR1 cells. Treatment of PR1 cells with bFGF increased the activity of Ras p21, while overexpression of a dominant negative mutant of Ras p21 abrogated the bFGF-induced activation of MAP kinase p44/42 in these cells. Furthermore, the Src kinase inhibitor PP1 suppressed bFGF-induced activation of MAP kinase p44/42 in both enriched lactotropes and PR1 cells. The Src kinase inhibitor PP1 also reduced bFGF activation of Ras p21 and cell
proliferation in PR1 cells. On the other hand, the bFGF-induced activation of MAP kinase p44/42 in enriched lactotropes and PR1 cells was not affected by protein kinase C (PKC) inhibitors. These data suggest that bFGF induction of lactotropic cell proliferation is possibly mediated by activation of Src kinase, Ras p21and MAP kinase p44/42. In addition, estradiol-increased lactotropic cell proliferation may also involve reduction in the dopamine-activated lactotropic cell growth-inhibitory TGF-beta1 production due to altered D2-receptor splicing. Together these data not only provide information on the cellular actions of estradiol on lactotropes but also indicate the possibility of a novel growth-promoting action of estradiol on the pituitary tissues and possibly on other tissues. This new information is significant in understanding the etiology and treatment of hyperprolactinemia.
Impacts
These data support the concept that the cell-cell communication between the lactotropes and follicular stellate cells is critical for the development of pituitary prolactin-secreting tumors following large amount of estrogen exposure.
Publications
- Oomizu S, Chaturvedi K, Sarkar DK. (2004) Folliculostellate cells determine the susceptibility of lactotropes to estradiol mitogenic action. Endocrinology 145:1473-1480.
- Chaturvedi K, Sarkar DK. (2004) Role of Src Ras MAP kinase p44/42 pathway in the mediation of basic fibroblast growth factor action on lactotrope derived PR1 cell proliferation. Endocrinology (In Press).
|
Progress 01/01/02 to 12/31/02
Outputs
Studies conducted during the past year have resulted in increased understanding of the action of estradiol. First, we were able to identify a novel mechanism involving dopamine, G protein and TGF-beta1 that inhibits lactotrope proliferation and is inhibited by estradiol. Second, we began to unfold the mechanism by which TGF-beta3 increases lactotropic cell proliferation. We found that TGF-beta3 acts on lactotropes to stimulate b-FGF release possibly via activation of p42/44 MAP kinase. b-FGF also possibly activates PKC and MAP kinase pathways to regulate lactotrope cell proliferation. Additionally, we found that a large population of genes as revealed by DNA microarray might influence susceptibility to estradiol.
Impacts
We will continue to learn the mechanisms by which TGF-beta3 increases lactotropic cell growth by altering the communication between FS cells and lactotropes.
Publications
- Oomizu S., Reddy D.E., Yang L.H., Boyadjieva N, Howard T. and Sarkar D.K. (2002) Dopamine regulation of lactotropic cell growth is mediated by transforming growth factor beta-1. Annual Meeting of Endocrine Society, San Francisco, CA, June 19-22, 2002.
- Chaturvedi K. and Sarkar D.K. (2002) Involvement of P42/44 MAP kinase pathway in induction of b-FGF from folliculo-stellate cells in the presence of ethanol and TGF-beta3. Annual Meeting of the Research Society on Alcoholism (RSA), San Francisco, CA, June 28-July 3, 2002.
- Chaturvedi K., Fialokoff E. and Sarkar D.K. (2002) Role of mitogen activated protein kinase C in mediation of basic-fibroblast growth factor-stimulated proliferation of prolactin-secreting PR1 cells. 32nd Annual Meeting of the Society for Neuroscience, Orlando, FL, November 2-7, 2002.
|
Progress 01/01/01 to 12/31/01
Outputs
The focus of this project is to understand how estrogen promotes pituitary tumorigenesis. Estrogen-induced tumorigenesis has been described in several tissues, including the pituitary. The pituitary of Fischer-344 rats is particularly sensitive to the mitogenic actions of estrogen. These rats rapidly develop prolactin (PRL)-secreting adenomas (prolactinomas) in response to estradiol treatment. The pituitary hypersensitivity to estrogen observed in Fischer-344 rats has been correlated to several factors, but the mechanisms of increased responsiveness to estrogen are still not well understood. Using this animal model for in vivo and in vitro studies, we have been able to demonstrate that estradiol-induced prolactinoma formation is associated with a significant reduction in the expression of both TGF-B1 and the type II TGF-B receptor (TBR-II) in pituitary lactotropes. In addition to TGF-B1, lactotropes produces TGF-B3. We studied the production and actions of the TGF-B3
isoforms in lactotropes in the presence and absence of estradiol. We found that estrogen stimulates TGF-B3 production but inhibits TGF-B1 production. Unlike TGF-B1, TGF-B3 stimulates lactotropic cell proliferation in the presence of estrogen. Disruption of TGF-B3 production by TGF-B3 antisense treatment blocked estrogen-induced cell proliferation. The direct action of TGF-B isoforms is generally growth inhibitory on epithelial cells. However, in some cell types, TGF-B stimulates cell growth via a paracrine mechanism by increasing growth-stimulatory peptide growth factors. Whether or not such a mechanism exists in pituitary cell culture was also examined in this study. We found that TGF-B3 action is mediated via paracrine interactions with the folliculo-stellate (FS) cells of the anterior pituitary. In addition, it was observed that basic fibroblast growth factor (bFGF) is a mediator of TGF-B3 action on lactotropic cell proliferation. These data provide evidence for a novel mechanism
of TGF-B3 action involving cell-to-cell interaction in the anterior pituitary between lactotropes and FS cells. In a preliminary study, we have found that FS cells also increase the sensitivity of lactotropes to estrogen. We found that the pituitary of Sprague-Dawley rats that have low sensitivity to estrogen also haslower number of FS cells. When the pituitary of Sprague-Dawley rats was transplanted under the kidney capsule in the presence of FS cells, the lactotropes' sensitivity to estrogen was greatly increased. Studies are continuing so we may better understand how estrogen controls pituitary tumor growth and development.
Impacts
These data provide evidence for a novel role of FS cells in control of lactotropic growth and possibly tumor development.
Publications
- Hentges S and Sarkar DK 2001 Transforming growth factor B regulation of estradiol-induced prolactinomas. Recent Progress in Neuroendocrinology 22:340-363
- De A, Hentges S, Boyadjieva N, Sarkar DK 2001 Effect of antisense suppression of transforming growth factor-B3 on lactotropic cell proliferation. J Neuroendocrinology 13:324-327
- Sarkar DK, Oomizu S, Reddy DE, Yang LH, Boyadjieva N, De A, Howard T, Neve K, Pastorcic M, Hentges S 2001 Defect in dopamine-regulated TGF-B1 signaling in prolactin-secreting pituitary tumors (Submitted)
- Oomizu S and Sarkar DK 2001 Folliculo-stellate cells regulate pituitary lactotropic cell response to estradiol. Annual Meeting of Endocrine Society, Denver, June 20-22
- Grandison L and Sarkar DK 2002 Estrogen-induced gene expression in the anterior pituitary of Sprague Dawley and Fischer-344 rats: comparison by microarray analysis. Annual Meeting of Endocrine Society, San Francisco, June 19-22
- Oomizu S, Reddy DE, Yang LH, Boyadjieva N, Howard T, Sarkar DK 2002 Dopamine regulation of lactotropic cell growth is mediated by transforming growth factor beta-1 (TGF-B1). Annual Meeting of Endocrine Society, San Francisco, June 19-22
|
Progress 01/01/00 to 12/31/00
Outputs
The ovarian steroid estradiol is known to increase lactotropic cell proliferation in humans as well as in animals. Literature suggests that certain populations of humans are more susceptible to estradiol. A similar difference in estradiol susceptibility is also observed between different strains of laboratory rats. Recently, folliculo-stellate (FS) cells have been shown to regulate estradiol-mitogenic action on lactotropes by releasing b-FGF. Whether or not FS cells governs the lactotropes' susceptibility to estradiol is studied. Determination of FS cell numbers in situ pituitaries of high estradiol-responsive Fischer-344 female rats and low estrogen-responsive Sprague-Dawley female rats indicated that the pituitary of Fischer rats had significantly more FS cells than that of Sprague-Dawley rats. Estradiol treatment for 2 weeks did not change the number of FS cells in pituitaries of Fischer or Sprague-Dawley ovariectomized female rats. The influence of FS cells on
estradiol mitotic action on lactotropes was studied in pituitaries transplanted in kidney capsule with or without FS cells in Fischer ovariectomized rats. The mitotic action of estradiol on lactotropes in transplanted Fischer pituitaries was enhanced when these pituitaries were cotransplanted with FS cells. The mitotic response of lactotropes to estradiol was absent when Sprague-Dawley rat pituitary cells were tested in cultures. However, lactotropes of Sprague-Dawley rat pituitaries showed significant mitotic response to estradiol when the pituitary cells were cultured with FS cells. These data suggest that cell-cell interaction between FS cells and lactotropes regulates estradiol's mitogenic action on lactotropes and influences the susceptibility to estradiol. (Supported by NIH Grants AA-00220 and CA 77550, and NJAES-Hatch 06138 to DKS)
Impacts
The study conducted past year provided evidence that cell-cell interaction between FS cells and lactotropes regulates estradiol's mitogenic action on lactotropes and influences the susceptibility to estradiol. This is significant in understanding the etiology of prolactinomas.
Publications
- Oomizu S., Sarkar D.K. Folliculo-stellate cells regulate pituitary lactotropic cell response to estradiol. Proceeding Annual Meeting of Endocrine Society Denver, CO, June 20-22, 2001.
|
|