Subcellular shift of the hepatic growth hormone receptor with progression of hepatitis C virus-related chronic liver disease

Hepatic Tumor Formation in Adult Mice Developmentally Exposed to Organotin

BACKGROUND

Tributyltin (TBT) is a persistent and bioaccumulative environmental toxicant. Developmental exposure to TBT has been shown to cause fatty liver disease (steatosis), as well as increased adiposity in many species, leading to its characterization as an obesogen.

OBJECTIVE

We aimed to determine the long-term effects of developmental TBT exposure on the liver.

METHODS

C57BL/6J mice were exposed to a dose of TBT (0.5 mg / kg body weight per day; 3.07 μ M ) below the current developmental no observed adverse effect level (NOAEL) via drinking water, or drinking water alone, provided to the dam from preconception through lactation. Sires were exposed during breeding and lactation. Pups from two parity cycles were included in this study. Animals were followed longitudinally, and livers of offspring were analyzed by pathological evaluation, immunohistochemistry, immunoblotting, and RNA sequencing.

RESULTS

Developmental exposure to TBT led to increased adiposity and hepatic steatosis at 14 and 20 weeks of age and increased liver adenomas at 45 weeks of age in male offspring. Female offspring displayed increased adiposity as compared with males, but TBT did not lead to an increase in fatty liver or tumor development in female offspring. Liver tumors in male mice were enriched in pathways and gene signatures associated with human and rodent nonalcoholic fatty liver disease (NAFLD) and hepatocellular carcinoma (HCC). This includes down-regulation of growth hormone receptor (GHR) and of STAT5 signaling, which occurred in response to TBT exposure and preceded liver tumor development.

CONCLUSIONS

These data reveal a previously unappreciated ability of TBT to increase risk for liver tumorigenesis in mice in a sex-specific manner. Taken together, these findings provide new insights into how early life environmental exposures contribute to liver disease in adulthood. https://doi.org/10.1289/EHP5414.

Increased nuclear expression of growth hormone receptor in uterine cervical neoplasms of women under 40 years old

There has been an increased incidence of cervical cancer among young women, and they tend to have a poor prognosis due to unknown reasons. We hypothesize growth hormone (GH) receptor (GHR) may be involved in the proliferation of cervical carcinoma, because GH-related neoplasms arise in various organs and the amount of GH secretion may be different according to age. GHR is normally expressed in the cell membrane and cytoplasm, while the nuclear distribution of GHR has been considered to reflect high proliferative activity of cells. We analyzed the subcellular localization of GHR by immunohistochemistry in cervical neoplasms of 55 patients (38.6 +/- 13.9 years old): 33 patients (< 40 years) and 22 patients (>or= 40 years). Nuclear expression of GHR was detected in more than 50% of neoplastic cells present in the tissue samples derived from 20 patients under 40 years (20/33, 61%), whereas less than 25% of neoplastic cells expressed GHR in their nuclei in 17 patients over 40 years (17/22, 77%). In contrast, more than 75% of neoplastic cells showed cytoplasmic GHR expression in the tissues derived from both age groups. Furthermore, the population of cells with nuclear GHR expression was high in the squamous epithelium and the stromal cells of patients under 40, but low in patients over 40. The GH-GHR signal may act at the nuclear level to promote the proliferation of uterine cervical neoplasms in young patients. We suggest the involvement of GHR in progression of uterine cervical carcinoma.

The extracellular domain of the growth hormone receptor interacts with coactivator activator to promote cell proliferation

The presence of GH receptor (GHR) in the cell nucleus correlates with cell division, and targeting the GHR to the nucleus results in constitutive proliferation and transformation because of increased sensitivity to autocrine GH. Here we have sought additional mechanisms that might account for the enhanced proliferation seen with nuclear GHR, commencing with a yeast two-hybrid (Y2H) screen for interactors with the extracellular domain of the GHR [GH-binding protein (GHBP)]. We find that the GHBP is a transcriptional activator in yeast and mammalian cells, and this activity resides in the lower cytokine receptor module. Activity is dependent on S226, the conserved serine of the cytokine receptor consensus WSXWS box. By using parallel GHBP affinity columns and tandem mass spectrometry of tryptic digests of proteins bound to wild-type GHBP and S226A columns, we identified proteins that bind to the transcriptionally active GHBP. These include a nucleoporin and two transcriptional regulators, notably the coactivator activator (CoAA), which is also an RNA binding splicing protein. Binding of CoAA to the GHBP was confirmed by glutathione S-transferase pulldown and coimmunoprecipitation, and shown to be GH dependent in pro-B Ba/F3 cells. Importantly, stable expression of CoAA in Ba/F3 cells resulted in an increased maximum proliferation in response to GH, but not IL-3. Because CoAA overexpression has been identified in many cancers and its stable expression promotes cell proliferation and cell transformation in NIH-3T3 cells, we suggest CoAA contributes to the proliferative actions of nuclear GHR by the hormone-dependent recruitment of this powerful coactivator to the GHR.

Hepatitis-C patients have reduced growth hormone (GH) secretion which improves during long-term therapy with pegylated interferon-alpha

OBJECTIVES

In vitro and in vivo data indicate multiple, but contradictory effects of interferon on pituitary hormone secretion. We therefore investigated prospectively basal and stimulated pituitary hormone secretion in 21 patients with chronic hepatitis C virus (HCV) infection before and during antiviral therapy.

METHODS

Twenty-one patients received pegylated interferon-alpha plus either ribavirin or levovirin. Baseline and stimulated growth hormone (GH), cortisol, luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin (PRL), and thyroid-stimulating hormone (TSH) responses were measured using standard pituitary function tests, before therapy in all and during therapy in 17 out of the 21 patients.

RESULTS

Before therapy 17 patients (81%) had severe GH insufficiency and 9 of these had low insulin-like growth factor-1 (IGF-1) concentrations. Basal and stimulated GH concentrations increased significantly during therapy, reducing the number of patients with severe GH insufficiency to four, but IGF-1 remained low. Basal PRL and TSH concentrations were normal before and during therapy, while thyroid-releasing hormone (TRH)-stimulated concentrations increased significantly during therapy. The adrenocorticotropic hormone (ACTH)/cortisol axis, basal and stimulated gonadotropin, and testosterone concentrations were normal throughout. Neither the HCV RNA level nor transaminases correlated with hormone concentrations before or during therapy.

CONCLUSIONS

GH insufficiency is common in patients with chronic HCV infection. While GH secretion improves during antiviral therapy, IGF-1 remains low, indicating persistent GH resistance of hepatocytes. Whether improvement in GH secretion during treatment is due to a direct drug effect or related to the suppression of viral load could not be differentiated, as most patients demonstrated a positive virologic response.

Recent advances in growth hormone signaling

Growth hormone (GH) is a major regulatory factor for overall body growth as evidenced by the height extremes in people with abnormal circulating GH levels or GH receptor (GHR) disruptions. GH also affects metabolism, cardiac and immune function, mental agility and aging. Currently, GH is being used therapeutically for a variety of clinical conditions including promotion of growth in short statured children, treatment of adults with GH deficiency and HIV-associated wasting. To help reveal previous unrecognized functions of GH, better understand the known functions of GH, and avoid adverse consequences that are often associated with exogenous GH administration, careful delineation of the molecular mechanisms whereby GH induces its diverse effects is needed. GH is a peptide hormone that is secreted into the circulation by the anterior pituitary and acts upon various target tissues expressing GHR. GH binding of GHR activates the tyrosine kinase Janus kinase 2 (JAK2), thus initiating a multitude of signaling cascades that result in a variety of biological responses including cellular proliferation, differentiation and migration, prevention of apoptosis, cytoskeletal reorganization and regulation of metabolic pathways. A number of signaling proteins and pathways activated by GH have been identified, including JAKs, signal transducers and activators of transcription (Stats), the mitogen activated protein kinase (MAPK) pathway, and the phosphatidylinositol 3'-kinase (PI3K) pathway. Although these signal transduction pathways have been well characterized, the manner by which GH activates these pathways, the downstream signals induced by these pathways, and the cross-talk with other pathways are not completely understood. Recent findings have added vital information to our understanding of these downstream signals induced by GH and mechanisms that terminate GH signaling, and identified new GH signaling proteins and pathways. This review will highlight some of these findings, many of which are unexpected and some of which challenge previously held beliefs about the mechanisms of GH signaling.