Opposing actions of intact and N-terminal fragments of the human prolactin/growth hormone family members on angiogenesis: An efficient mechanism for the regulation of angiogenesis

Abstract

Angiogenesis, the process of development of a new microvasculature, is regulated by a balance of positive and negative factors. We show both in vivo and in vitro that the members of the human prolactin͞growth hormone family, i.e., human prolactin, human growth hormone, human placental lactogen, and human growth hormone variant are angiogenic whereas their respective 16-kDa N-terminal fragments are antiangiogenic. The opposite actions are regulated in part via activation or inhibition of mitogen-activated protein kinase signaling pathway. In addition, the N-terminal fragments stimulate expression of type 1 plasminogen activator inhibitor whereas the intact molecules have no effect, an observation consistent with the fragments acting via separate receptors. The concept that a single molecule encodes both angiogenic and antiangiogenic peptides represents an efficient model for regulating the balance of positive and negative factors controlling angiogenesis. This hypothesis has potential physiological importance for the control of the vascular connection between the fetal and maternal circulations in the placenta, where human prolactin, human placental lactogen, and human growth hormone variant are expressed.Prolactin (PRL), growth hormone (GH), and placental lactogen (PL) are homologous protein hormones believed to have arisen from a common ancestral gene (1). PRL participates in the regulation of reproduction, osmoregulation, and immunomodulation (2, 3) whereas GH is involved in regulating growth and morphogenesis (4). Human (h) GHs, unlike other mammalian GHs, bind to the PRL receptor and thus display PRL-like activity; however, hPRL does not bind to the hGH receptor (5). PRL and GH are produced mainly by the anterior pituitary in all vertebrates. PRL is expressed also in lymphocytes and in the decidua (6). The human placenta expresses two structural homologs of hGH, hPL and a variant of hGH (hGH-V) (7). hGH-V rather than pituitary hGH is believed to regulate maternal metabolism during the second half of pregnancy. hPL is somatotropic in fetal tissues and contributes to stimulating mammary cell proliferation (8). Rodent placentas express and secrete several proteins whose biological activities are more PRL-like than GH-like; these include proliferin (PLF) and a proliferin-related peptide (PRP) (9).Members of the PRL͞GH family and derived peptides have been reported to both stimulate and inhibit angiogenesis. PLF expressed during the first half of pregnancy in the mouse is angiogenic whereas PRP expressed later in gestation is antiangiogenic. These findings suggest that PLF and PRP might play a role in initiating and stopping placental neovascularization (9). Human GH was reported to be angiogenic in vitro (10) whereas both bovine and chicken GH were shown to be angiogenic in vivo (11). We have shown that the 16-kDa N-terminal fragments (16K) of rat PRL and hPRL are antiangiogenic both in vitro (12) and in vivo (13). Rat PRL is cleaved by cathepsin D (14) to yield a 16-kDa N-terminal fragment and a 7-kDa C...

Potential roles of decidual prolactin in early pregnancy

“…In addition, expression of the prolactin gene is detected in capillary endothelial cells, and prolactin acts in an autocrine−paracrine fashion to regulate cellular proliferation (Clapp et al, 1998). The opposite actions of the intact and 16 kDa cleaved fragment are mediated by independent receptors rather than by competition for binding to the same receptor (Struman et al, 1999). Ligand binding and chemical crosslinking studies confirm that the 16 kDa prolactin fragment but not the 23 kDa prolactin binds to high affinity saturable sites in endothelial cell membranes, which are distinct in size from the cloned prolactin receptors (Clapp and Weiner, 1992).…”

“…Prolactin stimulates and inhibits angiogenesis: the intact prolactin molecule is angiogenic and its N-terminal 16 kDa fragment is anti-angiogenic (Struman et al, 1999). In addition, expression of the prolactin gene is detected in capillary endothelial cells, and prolactin acts in an autocrine−paracrine fashion to regulate cellular proliferation (Clapp et al, 1998).…”

Big Prolactin 60 kDa is Overexpressed in Salivary Glandular Epithelial Cells from Patients with Sjögren's Syndrome

“…We also demonstrated that synthesis of a 16-kDa prolactin slightly increased in SS patients. 16-kDa prolactin is the result of the enzymatic cleavage of 22-kDa prolactin (Mittra, 1980), and it has recently been found that the 16-kDa compound has an antiangiogenic effect (Struman et al, 1999). The presence of PRL receptors was shown in striated duct cells using either anti-PRL-receptor or anti-S100A6 antibodies.…”

EGF stimulates Pit-1 independent transcription of the human prolactin pituitary promoter in human breast cancer SK-BR-3 cells through its proximal AP-1 response element

“…Rabbit polyclonal antibodies were obtained (Eurogentec, Seraing, Belgium) using bacterially expressed and purified hPRL 16 kDa fragment (Struman et al, 1999) and shown to recognize the 23 kDa hPRL. These and monoclonal anti-phospho-JNK (Santa Cruz Biotechnology, Santa Cruz, CA) were used for immunofluorescence staining analysis.…”