Endocytosis and Degradation of Pegvisomant and a Potential New Mechanism That Inhibits the Nuclear Translocation of GHR

A Novel Mechanism of hPRL-G129R, a Prolactin Antagonist, Inhibits Human Breast Cancer Cell Proliferation and Migration

Prolactin (PRL) and its receptor, PRLR, are closely related to the occurrence and development of breast cancer. hPRL-G129R, an hPRLR antagonist, has been found to induce apoptosis in breast cancer cells via mechanisms currently unknown. Recent studies have indicated that PRLR exhibits dual functions based on its membrane/nucleus localization. In that context, we speculated whether hPRL-G129R is a dual-function antagonist. We studied the internalization of the hPRLR-G129R/PRLR complex using indirect immunofluorescence and Western blot assays. We found that hPRL-G129R not only inhibited PRLR-mediated intracellular signaling at the plasma membrane, but also blocked nuclear localization of the receptor in T-47D and MCF-7 cells in a time-dependent manner. Clone formation and transwell migration assays showed that hPRL-G129R inhibited PRL-driven proliferation and migration of tumor cells in vitro. Further, we found that increasing concentrations of hPRL-G129R inhibited the nuclear localization of PRLR and the levels of signal transducer and activator of transcription (STAT) 5 in tumor-bearing mice and hPRL-G129R also exerted an antiproliferative effect in vivo. These results indicate that hPRL-G129R is indeed a dual-function antagonist. This study lays a foundation for exploring and developing highly effective agents against the proliferation and progression of breast malignancies.

Different isoforms of growth hormone (20 kD-GH and 22 kD-GH) shows different biological activities in mesenchymal stem cell (MSC)

There are two main types of growth hormone (GH) in the circulatory system. One is 22 kD-GH, which is the predominant isoform in the circulating system, 90% GH is present as a 22 kD protein, and 10% of GH is present as a 20 kD protein. Amino acid sequences are identical between 20 kD-GH and 22 kD-GH protein, except that 20 kD-GH lacks 15 amino acid residues 32 to 46. Studies have shown that GH has many important biological effects on mesenchymal stem cells (MSCs). However, so far, the cellular characteristics of the two types of GH have not been studied in BM-MSCs. Furthermore, the biological activity of 20 kD-GH has not been explored in BM-MSCs. For this, in the current work, BM-MSCs were used as in vitro cell model. We have carried out the current research using a series of experimental techniques (such as Western-blot and indirect immunofluorescence). Firstly, we explored the cell behavior of two types of GH in the Bm-MSC model and found that they showed different biological characteristics; Secondly, we investigated the biological characteristics of 20 kD-GH and 22 kD-GH, and results showed that 22 kD-GH and 20 kD-GH exhibited different signaling profiles; Thirdly, we found that the 20 kD-GH and 22 kD-GH Gexhibited different regulatory effects on the osteogenic differentiation of BM-MSCs. The current research lays a solid foundation for further studies on the regulatory effects of GH on MSCs.

The nuclear-localized GHR is involved in the cell proliferation of gastric cancer, and pegvisomant may be an important potential drug to inhibit the proliferation of gastric cancer cells

Under normal physiological conditions, growth hormones (GH) play an important role in body growth and metabolism. A recent study showed that GH has important biological effects on gastric cancer (GC) both in vitro and in vivo. However, the biological properties of GH/GHR (GHR, growth hormone receptor) in GC cells have not been fully elucidated. To this end, we systemically studied the biological properties of GH in GC cells and found that GH/GHR was transported into the nuclei of GC cells. Furthermore, we investigated the functions of nuclear GHR and its potential mechanisms of action. We found that nuclear-localized GHR was closely related to the proliferation of GC cells. In addition, we systematically studied the effect of a GHR inhibitor (pegvisomant) on GC in vivo and in vitro, and the results showed that pegvisomant can not only inhibit the proliferation of GC cells but also inhibit the nuclear localization of GHR, suggesting that pegvisomant may be a dual-effect antagonist. Current research indicates that GHR may be a potential target for the treatment of GC.

Circadian clock disruption attenuated growth hormone(GH)-mediated signalling

The circadian molecular clock is an internal time-keeping system, which regulates various physiological processes through the generation of approximately 24-hour circadian rhythms. BMAL1 (brain and muscle arnt-like 1) is a core component of the circadian clock. Previous studies have shown that the circadian clock correlates with rhythmic secretion of endocrine hormone (such as growth hormone, GH). Currently, the effect of circadian clock on the GH-mediated biological activities is not fully understood. In this work, we used BMAL1 gene knockout mice (BMAL^-/- mice) model to explore the effect of circadian clock dysfunction on GH's activities, and the results from in vivo and in vitro experiments showed that GH-induced signaling is down-regulated. In vivo, GH/GHR-mediated tyrosine phosphorylation of signaling molecules (such as the Janus kinase-signal transducer and activator of transcription, JAK-STAT) in BMAL^-/- mice was significantly lower compared to control mice. In vitro, GH/GHR-mediated signaling in the hepatocytes from BMAL^-/- mice is decreased compared to hepatocytes from control mice. Furthermore, we explore the mechanism by which GH/GHR-mediated signalling is down-regulated in BMAL^-/- mice, and results indicated that the expression levels of negative regulators of cytokine signaling (such as the suppressor of cytokine signaling (SOCS) and protein phosphatase) were increased, which may be one of the factors that cause the GH signaling downregulation. In summary, our results show that the circadian clock affects the biological activities of GH. This finding lays the foundation for future investigations into the relationship between the circadian clock and biological activities of GH.

Acute sleep deprivation leads to growth hormone (GH) resistance in rats

Sleep is an essential physiological process that is required by all higher animals. Sleep has many important physiological functions. Previous studies have focused on the relationship between sleep and growth hormone secretion patterns. However, to date, whether sleep affects the biological activities of GH remains unclear. Here, we investigated this issue by evaluating the growth hormone receptor (GHR)-mediated intracellular signalling pathway in a sleep-deprived rat model. The results showed that GH's signalling ability is decreased in an acute sleep deprivation rat model. JAK2-STAT signalling was decreased significantly compared to that in control rats. We further analysed the possible molecular mechanism of GH signal inhibition in sleep-deprived rats. The results showed that the protein expression levels of SOCS3 (suppressors of cytokine signalling 3, which functions as the negative regulatory molecule of GH's signalling) increased; however, other negative regulatory proteins, such as protein phosphatase (PTP1B), did not change. In addition, acute sleep deprivation results in a significant increase in serum FFA (free fatty acid) level, which is also one of the factors contributing to GH inhibition. These findings suggest that GH signal resistance may be caused by a combination of factors. This study could serve as an important reference for related studies on the effect of sleep deprivation on endocrine systems.

Different cellular properties and loss of nuclear signalling of porcine epidermal growth factor receptor with aging

Epidermal growth factor (EGF) has important physiological functions that are mediated by the epidermal growth factor receptor (EGFR); however, to date, the changes in cellular behaviours and signalling properties of EGF/EGFR with aging remain unclear in the pig tissue models. Hence, the present study used porcine hepatocytes as a model to explore this issue. The study revealed the following results: 1) EGF could activate the intra-cellular signalling pathways in a time- and dose-dependent manner both in the young- and aged-pig hepatocytes, EGF induced tyrosine phosphorylation of EGFR, signal transducers and activators of transcription 3 (STAT3), protein kinase B (AKT) and extra-cellular signal-regulated kinase 1/2 (ERK1/2). Nevertheless, the EGF's signalling ability in the aged-pig hepatocytes was significantly reduced compared with that of the young-pig hepatocytes; 2) although EGF/EGFR can still be internalised into cells in a time-dependent manner with aging, the endocytic pathway differs between the young- and aged-pig hepatocytes. Furthermore, the results of the present study indicated that caveolin may play a pivotal role in the endocytosis of EGF/EGFR in the aged-pig hepatocytes, which is different from that of EGF/EGFR's endocytosis in young-pig hepatocytes; 3) It is well-known that EGFR carried out its biological effects via two signalling pathways, cytoplasmic pathway (traditional) and nuclear pathway; however, we found that the nuclear localisation of EGFR was significantly reduced in the aged-pig hepatocytes, which indicated that EGFR may lose its nuclear pathway with aging. Collectively, the present study lays the foundation for further study regarding the biological functional changes occurring in EGF/EGFR with aging.

Different intracellular signalling sensitivity and cell behaviour of porcine insulin with aging

Insulin has many important biological functions. Insulin interacts with the insulin receptor (IR) to play its physiological role and execute its functions. Here, we isolated porcine hepatocytes from young and aged pigs, which endogenously express the IR, as a model to study the intracellular signalling properties and cellular behaviour of insulin with aging. Firstly, we analysed the intracellular signal transduction that is triggered by insulin in porcine hepatocytes that were isolated from young and aged pigs and found that insulin can strongly activate insulin receptor subunit (IRS), protein kinase B (AKT), and GSK in a time- and dose-dependent manner in hepatocytes from young pigs. On the contrary, the signalling response to insulin in hepatocytes from aged pigs was significantly reduced compared to that of the young pig. Secondly, the different subcellular locations of insulin/insulin receptor (IR) may result in different biological activities, although nuclear-localized insulin/IR still could exhibit important functions and roles. We found that insulin can translocate into cell nuclei in the hepatocytes of the young pigs; however, insulin/insulin receptor fails to transports into the cell nucleus in hepatocytes from aged pigs, although insulin/insulin receptor could internalize into cell cytoplasm. In summary, in the current study, we explored and compared for the first time insulin's behaviour and signalling properties in the cells of young pig hepatocytes and aged pig hepatocytes. Furthermore, we found that the insulin signalling response in hepatocytes was significantly reduced with age; more importantly, we found that the cell behaviour of insulin was changed significantly in the hepatocytes from aged pigs compared to young pigs, and it is noteworthy that insulin/IR cannot translocate into the cell nuclei in the hepatocytes from the aged pig. This may be a potential new reason contributing to insulin resistance with aging, suggesting that we need to study the reason for insulin resistance from a new point of view.