Overexpression of parathyroid hormone-related protein promotes cell growth in the rat intestinal cell line IEC-6

Involvement of ERK1/2, p38 MAPK, and PI3K/Akt signaling pathways in the regulation of cell cycle progression by PTHrP in colon adenocarcinoma cells

Parathyroid hormone-related peptide (PTHrP) is distributed in most fetal and adult tissues, and its expression correlates with the severity of colon carcinoma. Recently we obtained evidence that in Caco-2 cells, a cell line from human colorectal adenocarcinoma, exogenous PTHrP increases the number of live cells, via ERK1/2, p38 MAPK, and PI3-kinase and induces the expression of cyclin D1, a cell cycle regulatory protein. In this study, we further investigated the role of PTHrP in the regulation of the cell cycle progression in these intestinal cells. Flow cytometry analysis revealed that PTHrP treatment diminishes the number of cells in the G0/G1 phase and increases the number in both S and G2/M phases. The hormone increases the expression of CDK6 and diminishes the amount of negative cell cycle regulators p27Kip1, p15INK4B, and p53. However, PTHrP does not modify the expression of cyclin D3, CDK4, and p16INK4A. In addition, inhibitors of ERK1/2 (PD98059), p38 MAPK (SB203580), and PI3Kinase (LY294002) reversed PTHrP response in Caco-2 cells. Taken together, our results suggest that PTHrP positively modulates cell cycle progression and changes the expression of proteins involved in cell cycle regulation via ERK1/2, p38 MAPK, and PI3K signaling pathways in Caco-2 cells.

PTHrP Overexpression Increases Sensitivity of Breast Cancer Cells to Apo2L/TRAIL

Parathyroid hormone-related protein (PTHrP) is a key component in breast development and breast tumour biology. PTHrP has been discovered as a causative agent of hypercalcaemia of malignancy and is also one of the main factors implicated in breast cancer mediated osteolysis. Clinical studies have determined that PTHrP expression by primary breast cancers was an independent predictor of improved prognosis. Furthermore, PTHrP has been demonstrated to cause tumour cell death both in vitro and in vivo. Apo2L/TRAIL is a promising new anti-cancer agent, due to its ability to selectively induce apoptosis in cancer cells whilst sparing most normal cells. However, some cancer cells are resistant to Apo2L/TRAIL-induced apoptosis thus limiting its therapeutic efficacy. The effects of PTHrP on cell death signalling pathways initiated by Apo2L/TRAIL were investigated in breast cancer cells. Expression of PTHrP in Apo2L/TRAIL resistant cell line MCF-7 sensitised these cells to Apo2L/TRAIL-induced apoptosis. The actions of PTHrP resulted from intracellular effects, since exogenous treatment of PTHrP had no effect on Apo2L/TRAIL-induced apoptosis. Apo2L/TRAIL-induced apoptosis in PTHrP expressing cells occurred through the activation of caspase-10 resulting in caspase-9 activation and induction of apoptosis through the effector caspases, caspase-6 and -7. PTHrP increased cell surface expression of Apo2L/TRAIL death receptors, TRAIL-R1 and TRAIL-R2. Antagonistic antibodies against the death receptors demonstrated that Apo2L/TRAIL mediated its apoptotic signals through activation of the TRAIL-R2 in PTHrP expressing breast cancer cells. These studies reveal a novel role for PTHrP with Apo2L/TRAIL that maybe important for future diagnosis and treatment of breast cancer.

Effects of parathyroid hormone-related protein and macrophage inflammatory protein-1α in Jurkat T-cells on tumor formation in vivo and expression of apoptosis regulatory genes in vitro

Parathyroid hormone-related protein (PTHrP) and macrophage inflammatory protein-1α (MIP-1α) have been implicated in the pathogenesis of adult T-cell leukemia/lymphoma, but their effects on T-cells have not been well studied. Here we analyzed the functions of PTHrP and MIP-1α on T-cell growth and death both in vitro and in vivo by overexpressing either factor in human Jurkat T-cells. PTHrP or MIP-1α did not affect Jurkat cell growth in vitro, but PTHrP increased their sensitivity to apoptosis. Importantly, PTHrP and MIP-1α decreased both tumor incidence and growth in vivo. To investigate possible mechanisms, polymerase chain reaction (PCR) arrays and real-time reverse transcription (RT)-PCR assays were performed. Both PTHrP and MIP-1α increased the expression of several factors including signal transducer and activator of transcription 4, tumor necrosis factor α, receptor activator of nuclear factor κB ligand and death-associated protein kinase 1, and decreased the expression of inhibitor of DNA binding 1, interferon γ and CD40 ligand in Jurkat cells. In addition, MIP-1α also increased the expression of transcription factor AP-2α and PTHrP increased expression of the vitamin D3 receptor. These data demonstrate that PTHrP and MIP-1α exert a profound antitumor effect presumably by increasing the sensitivity to apoptotic signals through modulation of transcription and apoptosis factors in T-cells.

Coherent expression chromosome cluster analysis reveals differential regulatory functions of amino-terminal and distal parathyroid hormone-related protein domains in prostate carcinoma

Parathyroid hormone-related protein (PTHrP) has a number of cancer-related actions. While best known for causing hypercalcemia of malignancy, it also has effects on cancer cell growth, apoptosis, and angiogenesis. Studying the actions of PTHrP in human cancer is complicated because there are three isoforms and many derived peptides. Several peptides are biologically active at known or presumed cell surface receptors; in addition, the PTHrP-derived molecules can exert effects at the cell nucleus. To address this complexity, we studied gene expression in a DU 145 prostate cancer cell line that was stably transfected with control vector, PTHrP 1-173 and PTHrP 33-173. With this model, regulatory effects of the amino-terminal portion of PTHrP would result only from transduction with the full-length molecule, while effects pertaining to distal sequences would be evident with either construct. Analysis of the expression profiles by microarrays demonstrated nonoverlapping groups of differentially expressed genes. Amino-terminal PTHrP affected groups of genes involved in apoptosis, prostaglandin and sex steroid metabolism, cell-matrix interactions, and cell differentiation, while PTHrP 33-173 caused substantial increases in MHC class I antigen expression. This work demonstrates the distinct biological actions of the amino-terminus compared to distal mid-molecule or carboxy-terminal sequences of PTHrP in prostate carcinoma cells and provides targets for further study of the malignant process.

PTHrP increases xenograft growth and promotes integrin alpha6beta4 expression and Akt activation in colon cancer

Parathyroid hormone-related protein (PTHrP) is expressed by human colon cancer tissue and cell lines. Expression of PTHrP and phosphatidylinositol 3-kinase (PI3-K) pathway components correlates with the severity of colon carcinoma. Here we observed a positive effect of endogenous PTHrP on LoVo (human colon cancer) cell proliferation, migration, invasion, integrin alpha6 and beta4 expression, and p-Akt levels. There was a direct correlation between PTHrP expression and anchorage-independent cell growth. PTHrP significantly increased xenograft growth; tumors from PTHrP-overexpressing cells showed increased expression of integrins alpha6 and beta4, and PI3-K pathway components. The higher expression of PTHrP in human colon cancer adenocarcinoma vs. normal colonic mucosa was accompanied by increased integrin alpha6 and beta4 levels. Elevated PTHrP expression in colon cancer may thus upregulate integrin alpha6beta4 expression, with consequent PI3-K activation. Targeting PTHrP might result in effective inhibition of tumor growth, migration, and invasion.

Increased cell survival, migration, invasion, and Akt expression in PTHrP-overexpressing LoVo colon cancer cell lines

Parathyroid hormone-related protein (PTHrP) has been localized in human colon cancer tissue and cell lines. We have previously shown that PTHrP increases colon cancer cell proliferation, extracellular matrix adhesion, and cell-surface integrin alpha6beta4 expression. Since cancer cell migration, invasion, and survival are crucial components of metastasis, and colon cancer has a high metastatic potential, in this study we used the human colon cancer cell line LoVo as a model system to study the effects of PTHrP on these parameters. PTHrP expression was modulated by stable transfection with a construct expressing PTHrP (-36 to +139). We report that PTHrP increases cell migration, invasion, and survival. PTHrP altered cell morphology, with PTHrP-overexpressing cells exhibiting increased spreading and several long protrusions. PTHrP also increased the steady-state mRNA levels of the integrin alpha6 and beta4 subunits, indicating a direct and/or indirect effect of PTHrP on the transcriptional and/or post-transcriptional regulation of integrin alpha6 and beta4 expression. Integrin alpha6beta4 activates the phosphoinositol 3-kinase (PI3-K)/Akt pathway, leading to glycogen synthase kinase-3 (GSK-3) deactivation. PTHrP overexpression also led to an increase in active Akt and inactive GSK-3 levels, indicating that the PTHrP-mediated upregulation of integrin alpha6beta4 expression may activate the PI3-K pathway, resulting in increased cell survival, migration and invasion.

Parathyroid hormone-related protein in human renal cell carcinoma

Parathyroid hormone-related protein (PTHrP), a polyprotein discovered in 1987, plays crucial roles not only in development and in various physiological events associated with normal life, but also in a number of pathological conditions such as cancer. PTHrP appears as the major causative agent in humoral hypercalcemia of malignancy (HHM) associated to a broad range of tumors. However, this is only one aspect of the multiple facets of PTHrP in cancer biology. Indeed, the complex growth factor-like properties of PTHrP has shed new light onto potential roles of this peptide in the regulation of tumor growth and invasion. Initial studies in breast, prostate and lung cancer and recent results in renal cell carcinoma (RCC) suggest such roles and highlight the therapeutic potential of PTHrP-targeting strategies in human cancer including RCC. In this review, the role of PTHrP in RCC tumorigenesis and its potential as a therapeutic target will be discussed.

PTH-related protein enhances LoVo colon cancer cell proliferation, adhesion, and integrin expression

Parathyroid hormone-related protein (PTHrP) has been localized in human colon cancer tissue and cell lines. Tumor cell adhesion to extracellular matrix (ECM) proteins plays a major role in the invasion and metastasis of tumor cells, and is mediated via integrin subunits. The LoVo human colon cancer cell line was used as a model system to study the effects of PTHrP on cell proliferation and adhesion to ECM proteins found in normal liver. Clones of LoVo cells engineered to overexpress PTHrP by stable transfection with a PTHrP cDNA showed enhanced cell proliferation vs. control (empty vector-transfected) cells. PTHrP-overexpressing cells also showed significantly higher adhesion to collagen type I, fibronectin, and laminin, and enhanced expression of the [symbol: see text] integrin subunits. These results indicate that PTHrP may play a role in colon cancer invasion and metastasis by increasing cell proliferation and adhesion to the ECM via upregulation of proinvasive integrin expression.

Age-related changes in the response of intestinal cells to parathyroid hormone

The concept of the role(s) of parathyroid hormone (PTH), has expanded from that on acting on the classical target tissues, bone and kidney, to the intestine where its actions are of regulatory and developmental importance: regulation of intracellular calcium through modulation of second messengers and, activation of mitogenic cascades leading to cell proliferation. Several causes have been postulated to modify the hormone response in intestinal cells with ageing, among them, alterations of PTH receptor (PTHR1) binding sites, reduced expression of G proteins and hormone signal transduction changes. The current review summarizes the actual knowledge regarding the molecular and biochemical basis of age-impaired PTH receptor-mediated signaling in intestinal cells. A fundamental understanding of why PTH functions are impaired with age will enhance our understanding of its importance in intestinal cell physiology.

Parathyroid hormone-related protein and lung biology

Parathyroid hormone-related protein (PTHrP) is expressed in normal and malignant lung and has roles in development, homeostasis, and pathophysiology of injury and cancer. Its effects in developing lung include regulation of branching morphogenesis and type II cell maturation. In adult lung, PTHrP stimulates disaturated phosphatidylcholine secretion, inhibits type II cell growth, and sensitizes them to apoptosis. In lung cancer, PTHrP may play a role in carcinoma progression, or metastasis. The protein could be a useful marker for assessing lung maturity or type II cell function, predicting risk of injury, and detecting lung cancer. PTHrP-based therapies could also prove useful in lung injury and lung cancer.

Proapoptotic effects of parathyroid hormone-related protein in type II pneumocytes

Parathyroid hormone-related protein (PTHrP) promotes or suppresses apoptosis in various settings depending on cell type and context. PTHrP 1-34 and PTHrP 67-86 are type II cell growth factors with effects on pneumocyte growth and surfactant secretion. This study investigated the effects of 24 h pretreatment with these two peptides on rat type II cell apoptosis after 0.3 J/cm2 ultraviolet-B irradiation. Adherent cells decreased in number by 15 +/- 5% and nonadherent cells increased > 5-fold 24 h after ultraviolet irradiation. Cell loss was due predominantly to apoptosis, based on ethidium bromide exclusion, nuclear condensation, and caspase 3 activity. Nuclear condensation increased from 15.6 +/- 2.2% of irradiated cells with no treatment to 25.6 +/- 4.9 and 22.9 +/- 1.8% of cells in ultraviolet/PTHrP 1-34 and ultraviolet/PTHrP 67-86 groups, respectively (P < 0.01), along with a 60% increase in caspase 3 activity. Effects on apoptosis were unaffected by the presence or absence of serum, but were ameliorated by growth to confluence or adherence to fibronectin. PTHrP 1-34 and PTHrP 67-86 augmented inositol phosphate levels, but had minimal effects on cAMP. Thus, PTHrP 1-34 and PTHrP 67-86 sensitize type II cells to apoptosis, possibly by a phospholipase C-dependent mechanism. The effects appear to be regulated by cell-matrix and cell-cell interactions.

Parathyroid hormone-related protein (PTHrP): a nucleocytoplasmic shuttling protein with distinct paracrine and intracrine roles

Parathyroid hormone-related protein (PTHrP) was first discovered as a circulating factor secreted by certain cancers responsible for the syndrome of humoral hypercalcemia of malignancy. PTHrP possesses distinct paracrine and intracrine signaling roles. The similarity of its N-terminus to that of parathyroid hormone (PTH) enables it to share PTH's paracrine signaling properties, whereas the rest of the molecule possesses other functions, largely relating to an intracrine signaling role in the nucleus/nucleolus in regulating apoptosis and cell proliferation. Recent advances have shown that intracellularly expressed PTHrP is able to shuttle in cell-cycle- and signal-dependent fashion between nucleus and cytoplasm through the action of the distinct intracellular transport receptors importin beta 1 and exportin 1 (Crm1) mediating nuclear import and export of PTHrP, respectively. Together, the import and export pathways constitute an integrated system for PTHrP subcellular localization. Intriguingly, PTHrP nuclear/nucleolar import is dependent on microtubule integrity, transport to the nucleus appearing to occur in vectorial fashion along microtubules, mediated in part by the action of importin beta 1. PTHrP has recently been shown to be able to bind to RNA, meaning that PTHrP's nucleocytoplasmic shuttling ability may relate to a specific role within the nucleus/nucleolus to regulate RNA synthesis and/or transport.

Parathyroid hormone-related protein upregulates integrin expression via an intracrine pathway in PC-3 prostate cancer cells

Parathyroid hormone-related protein (PTHrP) is expressed by human prostatic tissue and prostate cancer cell lines, and enhances prostate tumor cell growth both in vivo and in vitro. PTHrP expression also plays a role in the development of bone metastasis, which is a frequent complication in patients with prostate carcinoma. Tumor cell adhesion to extracellular matrix (ECM) components is mediated via integrin subunits, and plays a major role in the invasion and metastasis of tumor cells. We previously showed that PTHrP overexpression increases adhesion of the human prostate cancer cell line PC-3 to the ECM molecules collagen type I, fibronectin, and laminin. Increased adhesion is accompanied by upregulation in the expression of alpha1, alpha5, alpha6, and beta4 integrin subunits. We used the same cell line to study the mechanism via which PTHrP upregulates integrin expression. Clonal PC-3 cells were established overexpressing wild-type PTHrP or PTHrP mutated in the nuclear localization sequence (NLS). Mutation of the NLS negated the effects of PTHrP on alpha1, alpha5, alpha6, and beta4 integrin expression, indicating that these effects are mediated via an intracrine pathway requiring nuclear localization. Expression of the alpha2, alpha3, alphav, and beta1 integrin subunits were comparable in wild-type and NLS-mutated PTHrP transfectants. These findings indicate that PTHrP may play a role in prostate tumor invasion and metastasis by upregulating the expression of specific integrin subunits via an intracrine pathway.

Does PTH have a direct effect on intestine?

Dogma for the past three decades has dictated that parathyroid hormone (PTH) has no direct effect on intestine with regard to calcium or phosphate absorption, but rather that PTH acts to promote the synthesis of a hormonally active form of vitamin D, namely 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)]. However, diverse laboratories have each provided some evidence to suggest PTH does indeed have a direct effect on intestine. We will briefly review the evidence for biological effects, biochemical effects, and the presence of intestinal receptors for PTH, and conclude with the implications for biomedical research.

Parathyroid hormone-related protein enhances PC-3 prostate cancer cell growth via both autocrine/paracrine and intracrine pathways

Parathyroid hormone-related protein (PTHrP) is expressed by human prostatic tissue and prostate cancer cell lines, and positively influences primary prostate tumor growth in vivo. The human prostate cancer cell line PC-3, which expresses functional PTH/PTHrP receptors, was used as a model to study the effects of PTHrP on prostate cancer cell growth. Addition of PTHrP (1-34), (1-86), and (1-139) increased cell number and [3H]thymidine incorporation; these effects were reversed by anti-PTHrP antiserum. This antiserum also decreased endogenous PC-3 cell growth. Clonal PTHrP-overexpressing PC-3 cell lines also showed enhanced cell growth and [3H]thymidine incorporation and were enriched in the G2+M phase of the cell cycle, suggesting an effect of PTHrP on mitosis. Overexpression of PTHrP with the nuclear localization sequence (NLS) deletion partially reversed the growth-stimulatory effects. The growth rate of these cells was midway between that of wild-type PTHrP-overexpressing and control cells, presumably because NLS-mutated PTHrP is still secreted and acts through the cell surface PTH/PTHrP receptor. In contrast to NLS-mutated PTHrP, wild-type protein showed preferential nuclear localization. These results suggest that the proliferative effects of PTHrP in PC-3 cells are mediated via both autocrine/paracrine and intracrine pathways, and that controlling PTHrP production in prostate cancer may be therapeutically beneficial.