The basic route of the nuclear translocation porcine growth hormone (GH)-growth hormone receptor (GHR) complex (pGH/GHR) in porcine hepatocytes

The growth hormone receptor interacts with transcriptional regulator HMGN1 upon GH-induced nuclear translocation

Growth hormone (GH) actions are mediated through binding to its cell-surface receptor, the GH receptor (GHR), with consequent activation of downstream signalling. However, nuclear GHR localisation has also been observed and is associated with increased cancer cell proliferation. Here we investigated the functional implications of nuclear translocation of the GHR in the human endometrial cancer cell-line, RL95-2, and human mammary epithelial cell-line, MCF-10A. We found that following GH treatment, the GHR rapidly translocates to the nucleus, with maximal localisation at 5-10 min. Combined immunoprecipitation-mass spectrometry analysis of RL95-2 whole cell lysates identified 40 novel GHR binding partners, including the transcriptional regulator, HMGN1. Moreover, microarray analysis demonstrated that the gene targets of HMGN1 were differentially expressed following GH treatment, and co-immunoprecipitation showed that HMGN1 associates with the GHR in the nucleus. Therefore, our results suggest that GHR nuclear translocation might mediate GH actions via interaction with chromatin factors that then drive changes in specific downstream transcriptional programs.

Exosomes: Diagnostic and Therapeutic Implications in Cancer

Exosomes are a subset of extracellular vesicles produced by all cells, and they are present in various body fluids. Exosomes play crucial roles in tumor initiation/progression, immune suppression, immune surveillance, metabolic reprogramming, angiogenesis, and the polarization of macrophages. In this work, we summarize the mechanisms of exosome biogenesis and secretion. Since exosomes may be increased in the cancer cells and body fluids of cancer patients, exosomes and exosomal contents can be used as cancer diagnostic and prognostic markers. Exosomes contain proteins, lipids, and nucleic acids. These exosomal contents can be transferred into recipient cells. Therefore, this work details the roles of exosomes and exosomal contents in intercellular communications. Since exosomes mediate cellular interactions, exosomes can be targeted for developing anticancer therapy. This review summarizes current studies on the effects of exosomal inhibitors on cancer initiation and progression. Since exosomal contents can be transferred, exosomes can be modified to deliver molecular cargo such as anticancer drugs, small interfering RNAs (siRNAs), and micro RNAs (miRNAs). Thus, we also summarize recent advances in developing exosomes as drug delivery platforms. Exosomes display low toxicity, biodegradability, and efficient tissue targeting, which make them reliable delivery vehicles. We discuss the applications and challenges of exosomes as delivery vehicles in tumors, along with the clinical values of exosomes. In this review, we aim to highlight the biogenesis, functions, and diagnostic and therapeutic implications of exosomes in cancer.

The biological activity and signaling profile of EGF/EGFR were affected under heat stress conditions in IEC6 cells

Epidermal growth factor (EGF) is an effective cytoprotective peptide. It is the main nutritional factor involved in the development of the intestinal tract. It has many important biological effects on the intestinal mucosa. After binding to epidermal growth factor receptor (EGFR), it initiates a signal transduction cascade to jointly promote the migration, proliferation, and differentiation of various cell types. Heat stress severely affects the intestinal health of livestock and is becoming increasingly prevalent due to the yearly increase in ambient temperature and intestinal diseases. However, the effect of heat stress on the activity and signaling of EGF/EGFR in intestinal cells is still unclear. Therefore, rat intestinal crypt epithelial cell line (IEC6) was used as a model to explore this issue, and the results showed that EGF/EGFR is internalized into IEC6 cells in a time-dependent manner under physiological conditions. However, the activity of EGF/EGFR was altered under heat stress. Furthermore, we explored the effect of heat stress on EGF/EGFR-activated signaling transduction in IEC6 cells, and the results showed that levels of factors involved in EGFR-mediated intracellular signaling (such as EGFR, signal transducers and activators of transcription 3/protein kinase B, and extracellular regulatory kinase 1/2) were downregulated under heat stress. In summary, this study shows that heat stress could damage the biological activity and intracellular signaling of EGF/EGFR. These findings have scientific importance in the field of animal husbandry; and lay the foundation for the further study of the biological activities of EGF/EGFR in the intestine.

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 Cellular Behavior, Intracellular Signaling Profile and Nuclear-Targeted Potential Functions of Porcine Growth Hormone (pGH) in Swine Testicular Cells

Porcine growth hormone (pGH) has many important biological functions and roles, and the biological activity of pGH is closely related with its cell behavior and characteristics. However, so far, the behavior of pGH in swine testicular cell remains unclear. For this, in the current work, the swine testicular cell line (ST) was used as an in vitro model, and CLSM (Confocal laser scanning microscope), IFA (Indirect immunofluorescence assay), FCM (Flow cytometry) and WB (Western-blotting) were used to explore the pGH's cell behivior and function, and the results showed that pGH and GHR could internalize into ST cell and transported to the nucleus. Furthermore, we studied the internalization kinetics of pGH and GHR on ST cell, and found that pGH and GHR internalizes into ST cell in a time-dependent manner. More importantly, we also investigated the potential molecular functions of pGH-GHR after it entered into the cell nuclei. The results indicated that nuclear-localized GHR could participate in cell proliferation by regulating the signal intensity of STAT5. In summary, our current research shows that the nuclear-localized pGH-GHR participates in the cell proliferation of ST cell, which lays a solid foundation for further research on the regulatory effect of pGH on testicular tissue.

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.

22-kD growth hormone-induced nuclear GHR/STAT5/CyclinD1 signaling pathway plays an important role in promoting mesenchymal stem cell proliferation

Growth hormone (GH) exhibited the important biological activities in the mesenchymal stem cell (MSCs). However, the cellular behavior and properties of GH/GHR in MSCs remain unclear. A series of experiments (such as confocal laser scanning microscope [CLSM] and Western-blot) were performed to systematically investigate the cellular behavior of GH/GHR in MSCs, and the results showed that GH/GHR not only internalized into the cytoplasm, but also transported into the cell nuclei of MSCs. Furthermore, we studied the molecular mechanism by which GH/GHR internalized into cell, and the results indicated that clathrin plays more important role in the process of GHR internalization. More importantly, it can be found that nuclear-targeted GHR has the important biological functions in MSCs, which could promote MSCs proliferation. We further revealed the molecular mechanism by which nuclear-localized GHR regulates MSCs proliferation, and found that nuclear-targeted GHR enhanced the phosphorylation of STAT5, and the activated STAT5 initiates the transcription of CyclinD1, after which, the complex of CyclinD1 and CDK4 further phosphorylates Rb, and the activated Rb releases E2F1, the released E2F1 ultimately realizes the biological function of GH promoting cell proliferation. In short, in the current study，we used MSCs as a model to study the cellular behavior and properties of GH/GHR, and found that GH/GHR can internalize into cell cytoplasm and transport into the cell nuclei. Further work showed that nuclear GHR could drive cell proliferation via GHR/STAT5/CyclinD1 signaling pathway. The current research has laid an important foundation for further study on the regulatory effect of GH on MSCs.

The basic route of nuclear-targeted transport of IGF-1/IGF-1R and potential biological functions in intestinal epithelial cells

OBJECTIVES

Insulin-like growth factor (IGF-1) plays an important role in many biological processes in the intestinal tract. However, the cellular behaviour and characteristics of IGF-1/IGF-1R in intestinal cells remain unclear.

MATERIALS AND METHODS

A series of techniques (such as indirect immunofluorescence, co-localization and Western blot) have been used to systematically study the cellular behaviour of IGF-1/IGF-1R on intestinal cells.

RESULTS

We found that IGF-1 can not only internalize into the cytoplasm, but also transport into the cell nuclei. We systematically studied the detailed molecular pathways of IGF-1/IGF-1R's nuclear translocation. We found that IGF-1R underwent clathrin-mediated endocytosis into cells and then entered into Rab-5-positive endosomes. Dynein/dynactin were used as motors to drive Rab-5-positive endosomes carrying IGF-1R (cargo molecule) to Golgi apparatus (transit station) along the surface of the microtubule. IGF-1 and/or IGF-1R entered the cell nuclei through NPC (nuclear pore complex), a process mediated by NUP358. Further study indicated that nuclear localization of IGF-1 and/or IGF-1R promoted cell proliferation and increased the nuclear residence time of signalling molecules activated by IGF-1. Further experiments showed that IGF-1R may regulate the transcription of genes in the cell nuclei, indicating that nuclear-localized IGF-1R plays an important in cell proliferation.

CONCLUSIONS

In short, we revealed the molecular mechanism by which IGF-1/IGF-1R transports into the cell nuclei of intestinal cells. More importantly, the current work showed that the nuclear-localized IGF-1R has important biological functions.

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.

The NAE Pathway: Autobahn to the Nucleus for Cell Surface Receptors

Various growth factors and full-length cell surface receptors such as EGFR are translocated from the cell surface to the nucleoplasm, baffling cell biologists to the mechanisms and functions of this process. Elevated levels of nuclear EGFR correlate with poor prognosis in various cancers. In recent years, nuclear EGFR has been implicated in regulating gene transcription, cell proliferation and DNA damage repair. Different models have been proposed to explain how the receptors are transported into the nucleus. However, a clear consensus has yet to be reached. Recently, we described the nuclear envelope associated endosomes (NAE) pathway, which delivers EGFR from the cell surface to the nucleus. This pathway involves transport, docking and fusion of NAEs with the outer membrane of the nuclear envelope. EGFR is then presumed to be transported through the nuclear pore complex, extracted from membranes and solubilised. The SUN1/2 nuclear envelope proteins, Importin-beta, nuclear pore complex proteins and the Sec61 translocon have been implicated in the process. While this framework can explain the cell surface to nucleus traffic of EGFR and other cell surface receptors, it raises several questions that we consider in this review, together with implications for health and disease.

Zinc ions increase GH signaling ability through regulation of available plasma membrane-localized GHR

It is well known that zinc ion (Zn²⁺ ) can regulate the biological activity of growth hormone (GH). However, until now, the mechanism by which Zn²⁺ regulates GH biological activity remains unclear. In the current study, we first performed molecular docking between Zn²⁺ and porcine GH (pGH) using computational biology. We then explored the effect of Zn²⁺ on the GH signaling ability in the cell model expressing porcine growth hormone receptor (GHR). It was found that the phosphorylation levels of Janus kinase 2, signal transducers and activators of transcription 5/3/1, and GHR increased significantly under Zn²⁺ treatment, indicating that Zn²⁺ can enhance the signaling ability of GH/GHR. On this basis, we further explored how Zn²⁺ regulates the biological activity of GH/GHR. The results showed that downregulation and turnover of GHR changed under Zn²⁺ /pGH treatment. Zn²⁺ enhanced the membrane residence time of pGH/GHR and delayed GHR downregulation. Further investigation showed that the internalization dynamic of pGH/GHR was changed by Zn²⁺ , which prolonged the residence time of pGH/GHR in the cell membrane. These factors acted together to upregulate the signaling of GH/GHR. This study lays a foundation for further exploration of the biological effects of Zn²⁺ on GH.

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

CONTEXT

Pegvisomant, a growth hormone receptor (GHR) antagonist, is a well-known drug that was designed to treat acromegaly. However, recent studies have indicated that the GHR is a "moonlighting" protein that may exhibit dual functions based on its localization in the plasma membrane and nucleus. In light of this finding, we explored whether pegvisomant is a potential "moonlighting" GHR antagonist. In addition, the mechanisms of the endocytosis, postendocytic sorting, and degradation of pegvisomant are not fully understood.

OBJECTIVE

This study investigated whether pegvisomant is a "moonlighting" antagonist and explored the mechanisms of the endocytosis, postendocytic sorting, and degradation of pegvisomant.

METHODS

Indirect immunofluorescence and Western blot coupled with pharmacological inhibitors and gene silencing (small interfering RNA) were used to explore the mechanisms of the endocytosis, postendocytic sorting, and degradation of pegvisomant. Western blot, immunohistochemistry, and indirect immunofluorescence coupled with subcellular fractionation analysis were used to determine the effect of pegvisomant on GHR's nuclear localization in vitro and in vivo.

RESULTS

Here, we show that the endocytosis of pegvisomant is mainly mediated though the clathrin pathway. Further study of the postendocytic sorting of pegvisomant shows that pegvisomant enters into different types of endosomes under GHR mediation. In addition, GHR is slightly downregulated by pegvisomant; further study indicates that proteasomes and lysosomes may cooperate to regulate pegvisomant/GHR degradation. Most importantly, we show that pegvisomant inhibits the nuclear localization of GHR.

CONCLUSION

Our study showed that pegvisomant is a "moonlighting" antagonist. In addition, we revealed the mechanisms of the endocytosis, postendocytic sorting, and degradation of pegvisomant.

Identification of a novel antisense RNA that regulates growth hormone receptor expression in chickens

Natural antisense transcripts (NATs) are widely present in mammalian genomes and act as pivotal regulator molecules of gene expression. However, studies on NATs in the chicken are relatively rare. We identified a novel antisense transcript in the chicken, designated GHR-AS-EST, transcribed from the growth hormone receptor (GHR) locus, which encodes a well-known regulatory molecule of muscle development and fat deposition. GHR-AS-EST is predominantly expressed in the chicken liver and muscle tissues. GHR-AS-EST sequence conservation among vertebrates is weak. GHR-AS-EST forms an RNA-RNA duplex with GHBP to increase its stability, and regulates the expression of GHR sense transcripts at both the mRNA and protein levels. Further, GHR-AS-EST promotes cell proliferation by stimulating the expression of signaling factors in the JAK2/STAT pathway, and contributes to fat deposition via downregulating the expression of signaling factors in the JAK2/SOCS pathway in LMH hepatocellular carcinoma cells. We expect that the discovery of a NAT for a regulatory gene associated with cell proliferation and lipolysis will further our understanding of the molecular regulation of both muscle development and fat deposition.

Expression of growth hormone and growth hormone receptor genes in human eye tissues

In humans, the polygenic growth hormone (GH) locus is located on chromosome 17 and contributes with three types of proteins: pituitary GH which consists of at least two isoforms one of 22 kDa and the other of 20 kDa, placental GH, which also exhibits isoforms, and chorionic somatomammotropin hormone (CSH). While pituitary GH results from the expression of the GH-1 (GH-N) gene, placental GH is produced by the expression of the GH-2 (GH-V) gene and CSH is contributed by expression of the CSH-1 and CSH-2 genes. The location where GH-1 is expressed is the anterior pituitary and the rest of the genes in the locus are expressed in placenta. On the other hand, expression and synthesis of GH in extra-pituitary tissues, including the eye, has been recently described. However, the physiological role of GH in the eye has not yet been elucidated, although a possible neuroprotective role has been hypothesized. Thus, we analyzed GH-1, GH-2, CSH1/2, Pit-1, GHR, GHRH, GHRHR, SST, SSTR1, SSTR2, SSTR3, SSTR4, and SSTR5 to elucidate the expression and regulation of the GH locus in the human eye. Through qPCR analysis, we only found evidence of GH-1 expression in retina, choroid and trabecular meshwork; its transcript turned out to be the same as pituitary GH mRNA found in major species, and no splicing variants were detected. PIT1 was absent in all the ocular tissues implying an independent GH-1 expression mechanism. We found evidence of GHR in the cornea, choroid coat and retina. These results suggest autocrine and/or paracrine regulation, possibly exerted by GHRH and SSTs (since their mRNAs and receptors were found predominantly in retinal, choroidal and corneal tissues) since expression of both molecules was detected in different ocular tissues, as well as in the same tissues where GH-1 expression was confirmed. Our results add solid evidence about the existence of a regulatory local system for GH expression and release in the human eye.

Cellular internalization and trafficking of 20 KDa human growth hormone

Twenty kilodalton human growth hormone (20K-GH) is the second most abundant GH isoform after the twenty-two kilodalton human growth hormone (22 K-GH) isoform. 20K-GH exhibits similar but not identical physiological activities as that of 22K-GH. The cell behaviour of 22K-GH has been extensively studied, but little or no information has been reported regarding 20K-GH. Here, we focussed on the internalization of 20K-GH. We found that the internalization of 20K-GH is rapid and occurs in a time- and dose-dependent manner. 20K-GH internalization is mediated by GHR. It appears that the internalization of 20K-GH and GHR into the cytoplasm is mediated by clathrin and/or caveolin. The current study indicates that 20K-GH can internalize into the cytoplasm and suggests that the internalized 20K-GH may exhibit different functions from those of 22K-GH.