REGULATION OF KERATINOCYTE GROWTH FACTOR RECEPTOR AND ANDROGEN RECEPTOR IN EPITHELIAL CELLS OF THE HUMAN PROSTATE

Controlled dual release of dihydrotestosterone and flutamide from polycaprolactone electrospun scaffolds accelerate burn wound healing

Wound healing is a complex process involving multiple independent and overlapping sequential physiological mechanisms. In addition to cutaneous injury, a severe burn stimulates physiological derangements that induce a systemic hypermetabolic response resulting in impaired wound healing. Topical application of the anti‐androgen drug, flutamide accelerates cutaneous wound healing, whereas paradoxically systemic dihydrotestosterone (DHT) improves burn wound healing. We developed and characterized a PCL scaffold that is capable of controlled release of androgen (DHT) and anti‐androgen (F) individually or together. This study aims to investigate whether local modification of androgen actions has an impact on burn injury wound healing. In a full‐thickness burn wound healing, mouse model, DHT/F‐scaffold showed a significantly faster wound healing compared with F‐scaffold or DHT‐scaffold. Histology analysis confirmed that DHT/F‐scaffold exhibited higher re‐epithelization, cell proliferation, angiogenesis, and collagen deposition. Dual release of DHT and F from PCL scaffolds promoted cell proliferation of human keratinocytes and alters the keratinocyte cell cycle. Lastly, no adverse effects on androgen‐dependent organs, spleen and liver were observed. In conclusion, we demonstrated DHT plus F load PCL scaffolds accelerated burn wound healing when loading alone did not. These findings point to a complex role of androgens in burn wound healing and open novel therapeutic avenues for treating severe burn patients.

Androgen receptor CAG polymorphism and the risk of benign prostatic hyperplasia in a Brazilian population

Benign prostatic hyperplasia (BPH) is a very frequent age-related proliferative abnormality in men. Polymorphic CAG repeat in the androgen receptor (AR) can alter transactivation of androgen-responsive genes and potentially influence BPH risk. We investigated the association between CAG repeat length and risk of BPH in a case-control study of a Brazilian population. We evaluated 214 patients; 126 with BPH and 88 healthy controls. DNA was extracted from peripheral leucocytes and the AR gene was analyzed using fragment analysis. Hazard ratio (HR) and 95% confidence interval were estimated using logistic regression models. Mean CAG length was not different between patients with BPH and controls. The CAG repeat length was examined as a categorical variable (CAG ≤ 21 vs. CAG > 21 and CAG ≤ 22 vs. CAG > 22) and did not differ between the control vs. the BPH group. We found no evidence for an association between AR CAG repeat length in BPH risk in a population-based sample of Brazilians.

Androgen receptor GGC polymorphism and testosterone levels associated with high risk of prostate cancer and benign prostatic hyperplasia

Polymorphic GGC repeats in the androgen receptor (AR) gene can alter transactivation of androgen-responsive genes and increase the risk of benign prostatic hyperplasia (BPH) and prostate cancer (PCa). We investigated the association between GGC repeat length, testosterone levels and the risk of developing PCa and BPH in a population from southern Brazil. A sample comprising 130 PCa, 126 BPH and 88 control patients was evaluated. DNA was extracted from leukocytes and the AR gene was analyzed by fragment analysis. The hazard ratio (HR) was estimated. GGC mean length was not different between the three study groups. The risk of developing PCa in individuals with GGC > 19 was 3.300 (95 %CI 1.385-7.874) higher when compared to the GGC ≤ 19 group (p = 0.007). The risk of developing PCa and BPH in individuals with total testosterone levels <4 ng/mL was 2.799 (95 % CI 1.362-5.754). (p = 0.005) and 2.786 (95 % CI 1.470-5.280) (p = 0.002), respectively. Total testosterone levels in patients with GGC > 19 were significantly lower when compared to patients in the GGC ≤ 19 group. Our data suggest that the presence of a high number of polymorphic GGC repeats in the AR gene is associated with an increased risk of developing PCa and BPH, and that lower testosterone levels also increase the risk of developing these diseases.

Androgen-modulated p21 and p53 gene expression in human non-transformed epithelial prostatic cells in primary cultures

The prostate gland is under androgen control. The aim of the present study was to evaluate the expression of two genes that are regulators of the cell cycle, the p53 and p21 genes, in human non-transformed epithelial prostatic cells (HNTEPs) treated with different concentrations of hormones. Samples of prostate tissue were obtained from 10 patients between 60 and 77 years of age. HNTEP cells were grown in basal medium and treated with dihydrotestosterone (DHT) in different conditions for 4 h. A low concentration of DHT resulted in a significant increase in cell growth; this effect was eradicated by addition of the antiandrogen hydroxyflutamide. Furthermore, the low concentration of DHT induced lower mRNA levels in the p53 and p21 genes in HNTEP cells. In turn, high DHT concentrations induced a significant increase in the expression of the p53 and p21 genes. The present data suggest that the p53 and p21 genes play a role in the control of responsiveness and androgen dose-dependent cell proliferation in HNTEP cells. Further studies are required to assess the intracellular signaling pathway regulated by p53 and p21 under the influence of androgens and its implications for the pathophysiology of prostate diseases.

Lysyl oxidase propeptide inhibits prostate cancer cell growth by mechanisms that target FGF-2-cell binding and signaling

Enhanced RAS signaling and decreased androgen dependence of prostate cancer cells accompany poor clinical outcomes. Elevated autocrine FGF-2 signaling promotes prostate cancer cell growth and survival. Expression of lysyl oxidase (LOX) inhibits RAS transforming activity. LOX is secreted as 50 kDa pro-lysyl oxidase protein and then undergoes extracellular proteolytic processing to form ~30 kDa lysyl oxidase enzyme and ~18 kDa pro-peptide (LOX-PP). We have previously shown that LOX-PP inhibits breast cancer cell transformation and tumor formation, but mechanisms of action of LOX-PP have not been fully elucidated. Here we report that LOX expression is reduced in prostate cancer cell lines and that recombinant LOX-PP protein inhibits serum-stimulated DNA synthesis and MEK/ERK and PI3K/AKT pathways in DU 145 and PC-3 androgen-independent cell lines. In DU 145 cells, treatment with a pharmacologic FGF-receptor inhibitor or a neutralizing anti-FGFR1 antibody mimicked LOX-PP inhibition of serum-stimulated DNA synthesis. FGF-2-stimulated DNA synthesis, ERK1/2, AKT, and FRS2α activation were found all to be inhibited by LOX-PP in DU 145 cells. LOX-PP reduced specific binding of FGF-2 to DU 145 cells, suggesting that LOX-PP targets FGF signaling at the receptor. Interestingly, PC-3 cells did not respond to FGF-2, consistent with previous reports. We conclude that LOX-PP inhibits proliferation of DU 145 cells by interfering with FGFR(s) binding and signaling, and that LOX-PP has other mechanisms of action in PC-3 cells.

5alpha-dihydrotestosterone (DHT) retards wound closure by inhibiting re-epithelialization

The ongoing search for explanations as to why elderly males heal acute skin wounds more slowly than do their female counterparts (and are more strongly disposed to conditions of chronic ulceration) has identified endogenous oestrogens and androgens as being respectively enhancers and inhibitors of repair. We previously demonstrated that blocking the conversion of testosterone to 5alpha-dihydrotestosterone (DHT) limits its ability to impair healing, suggesting that DHT is a more potent inhibitor of repair than is testosterone. The present study aimed to delineate the central mechanisms by which androgens delay repair. Whilst the contractile properties of neither rat wounds in vivo nor fibroblast-impregnated collagenous discs in vitro appeared to be influenced by androgen manipulations, the global blockade of DHT biosynthesis markedly accelerated re-epithelialization of incisional and excisional wounds and reduced local expression of beta-catenin, a key inhibitor of repair. Moreover, DHT retarded the in vitro migration of epidermal keratinocytes following scratch wounding. By contrast, it failed to influence the migratory and proliferative properties of dermal fibroblasts, suggesting that its primary inhibitory effect is upon re-epithelialization. These novel findings may be of particular significance in the context of chronic ulceration, for which being male is a key risk factor.

Immunostaining of the androgen receptor and sequence analysis of its DNA-binding domain in canine prostate cancer

Prostate cancer in the dog (cPC) has many features in common with hormone refractory human prostate cancer. As cPC is seen more often in castrated dogs, the contribution of the androgen receptor (AR) to the development of prostate cancer remains questionable. The aim of the present study was to evaluate the presence of the AR by immunohistochemistry in cPC. AR staining was observed in most tumors from intact and castrated dogs, but the proportion of positive cells and the staining intensity were much lower than in the prostate of healthy, non-castrated dogs. Most of the positive staining was seen in the cytoplasm rather than in the nuclei of the tumor cells. The predominant cytoplasmic localization was not related to mutations in exon 3 of the DNA-binding domain of the AR, as shown by sequence analysis of microdissected AR positive tumor cells. Other mechanisms that lead to an impaired androgen-AR signaling or a basal/stem cell like origin may explain the low cytoplasmic AR staining in cPC.

Immunoexpression of androgen receptor in the nontumorous pituitary and in adenomas

Little information is available regarding androgen receptor immunoexpression (AR) in the normal and neoplastic human pituitary. Available experimental data links it to primarily gonadotroph cells. We undertook an immunohistochemical study of 41 autopsy-derived normal glands from patients of both sexes and all ages as well as 79 fully characterized pituitary adenomas of all types, the focus being upon AR expression in normal and neoplastic gonadotrophs. Nuclear AR immunoreactivity was noted in gonadotrophs and other normal adeno- and neurohypophysial cells. In addition to its presence in 74% of gonadotroph and 55% of null cell adenomas, lesser proportions of other adenoma types (adrenocorticotropic hormone 50%, prolactin 38%, growth hormone 33%) also exhibited AR immunoreactivity. No staining of thyroid-stimulating hormone adenomas was noted. The physiologic significance of our findings remains to be explored. The literature regarding AR expression in animal and human pituitaries is reviewed.

Enhanced paracrine FGF10 expression promotes formation of multifocal prostate adenocarcinoma and an increase in epithelial androgen receptor

Enhanced mesenchymal expression of FGF10 led to the formation of multifocal PIN or prostate cancer. Inhibition of epithelial FGFR1 signaling using DN FGFR1 led to reversal of the cancer phenotype. A subset of the FGF10-induced carcinoma was serially transplantable. Paracrine FGF10 led to an increase in epithelial androgen receptor and synergized with cell-autonomous activated AKT. Our observations indicate that stromal FGF10 expression may facilitate the multifocal histology observed in prostate adenocarcinoma and suggest the FGF10/FGFR1 axis as a potential therapeutic target in treating hormone-sensitive or refractory prostate cancer. We also show that transient exposure to a paracrine growth factor may be sufficient for the initiation of oncogenic transformation.

The role of androgen in determining differentiation and regulation of androgen receptor expression in the human prostatic epithelium transient amplifying population

Abnormal differentiation in epithelial stem cells or their immediate proliferative progeny, the transiently amplifying population (TAP), may explain malignant pathogenesis in the human prostate. These models are of particular importance as differing sensitivities to androgen among epithelial cell subpopulations during differentiation are recognised and may account for progression to androgen independent prostate cancer. Androgens are crucial in driving terminal differentiation and their indirect effects via growth factors from adjacent androgen responsive stroma are becoming better characterised. However, direct effects of androgen on immature cells in the context of a prostate stem cell model have not been investigated in detail and are studied in this work. In alpha2beta1hi stem cell enriched basal cells, androgen analogue R1881 directly promoted differentiation by the induction of differentiation-specific markers CK18, androgen receptor (AR), PSA and PAP. Furthermore, treatment with androgen down-regulated alpha2beta1 integrin expression, which is implicated in the maintenance of the immature basal cell phenotype. The alpha2beta1hi cells were previously demonstrated to lack AR expression and the direct effects of androgen were confirmed by inhibition using the anti-androgen bicalutamide. AR protein expression in alpha2beta1hi cells became detectable when its degradation was repressed by the proteosomal inhibitor MG132. Stratifying the alpha2beta1hi cells into stem (CD133(+)) and transient amplifying population (TAP) (CD133(-)) subpopulations, AR mRNA expression was found to be restricted to the CD133(-) (TAP) cells. The presence of a functional AR in the TAP, an androgen independent subpopulation for survival, may have particular clinical significance in hormone resistant prostate cancer, where both the selection of immature cells and functioning AR regulated pathways are involved.

Androgen receptor mutations are associated with Gleason score in localized prostate cancer

OBJECTIVE

To study human androgen receptor (hAR) mutations and their relationship to the clinical and pathological characteristics of patients with prostate cancer, as the mechanisms by which tumour cells escape androgen control and grow independently of hormone stimulation are unclear.

PATIENTS AND METHODS

In all, 67 radical prostatectomy specimens were sequenced genomically (mean age of the patients, 64 years; median prostate-specific antigen level 15 ng/mL; 34% T1 and 66% T2). Of the 66 patients who had a valid follow-up, 28 (43%) had biochemical progression during the follow-up.

RESULTS

There was mutation in the hAR in 11 patients (16%); nine types of different mutations were identified, only one of which was described previously in patients with prostate cancer. Patients with mutated hAR had statistically lower Gleason scores (P = 0.004) than had patients with native hAR.

CONCLUSION

hAR mutations have a different effect on the disease course in patients with localized than in those with metastatic prostatic cancer.

Molecular markers in the diagnosis of prostate cancer

The genetic alterations leading to prostate cancer are gradually being discovered. A wide variety of genes have been associated with prostate cancer development as well as tumor progression. Knowledge of gene polymorphisms associated with disease aid in the understanding of important pathways involved in this process and may result in the near future in clinical applications. Urinary molecular markers will soon be available to aid in the decision of repeat prostate biopsies. Recent findings suggest the importance of androgen signaling in disease development and progression. The further understanding of interaction of inflammation, diet, and genetic predisposition will improve risk stratification in the near future.

Effect of keratinocyte growth factor on cell viability in primary cultured human prostate cancer stromal cells

In normal prostate, keratinocyte growth factor (KGF), also known as fibroblast growth factor-7 (FGF-7) serves as a paracrine growth factor synthesized in stromal cells that acts on epithelial cells through its receptor, KGFR. KGF and KGFR were found in human cancer epithelial cells as well as stromal cells. Since KGF expressed in epithelial cells of benign prostatic hyperplasia (BPH) and in prostate cancer, it has been suggested that KGF might act as an autocrine factor in BPH and prostate cancer. To investigate the roles of KGF in cancerous stroma, primary cultured human prostate cancer stromal cells (PCSCs) were isolated and evaluated. These PCSCs possessed estrogen receptors and KGFR, but not androgen receptor as determined by RT-PCR and Western blot, respectively. KGF exhibited mitogenic and anti-apoptotic effects that correlated with induction of cyclin-D1, Bcl-2, Bcl-xL and phospho-Akt expression in PCSCs, where treatment with KGF antiserum abolished cell proliferation and anti-apoptotic protein expression. PCSCs exposed to KGF for various time periods resulted in phosphorylation of Akt and subsequent up-regulation of Bcl-2. KGF modulated dynamic protein expression indicated that KGF triggered cell cycle machinery and then activated anti-apoptotic actions in PCSCs. Cell proliferation analysis indicated that tamoxifen or ICI 182,780 reduced cell viability in a dose-dependent manner; however, KGF prevented this inhibition, which further demonstrated KGF triggered anti-apoptotic machinery through activating Bcl-2 and phospho-Akt expression. In summary, KGF has an autocrine effect and serves as a survival factor in primary cultured human prostate cancer stromal cells.

KGF suppresses α2β1 integrin function and promotes differentiation of the transient amplifying population in human prostatic epithelium

Prostate epithelial stem cells are self-renewing cells capable of differentiation into prostate epithelium, and are thought to contribute towards both benign and malignant conditions in the human prostate. We have previously demonstrated that prostate epithelial basal cells express high levels of integrin α2β1 and this population can be subdivided into stem (α2β1hi CD133+) and transient-amplifying population (TAP) cells (α2β1hi CD133-). However, the molecular mechanism(s) controlling the commitment and regulation of these cells towards differentiated epithelium remains unclear. Here, we demonstrate that β1 integrin function is required for the maintenance of basal prostatic epithelial cells and suppression of its function by either methylcellulose or, more specifically, β1-blocking antibody (80 μg/ml) induces differentiation, with associated expression of the differentiation-specific markers prostate acid phosphatase (PAP) and cytokeratin 18 (CK18). Keratinocyte growth factor (KGF), a stromal-derived growth factor, has previously been implicated in prostate organogenesis using in vitro tissue recombination experiments. We show that treatment with KGF (10 ng/ml) potently induces epithelial differentiation with concomitant suppression of α2β1 integrin expression as well as the induction of androgen receptor expression. Specifically, p38-MAPK appears to be involved and the presence of SB202190, a p38 inhibitor, significantly blocks KGF-induced differentiation. Furthermore, the expression of the high-affinity receptor tyrosine kinase to KGF (FGFR2) is predominantly detectable in α2β1hi CD133- TAP cells when compared with stem cells (α2β1hi CD133+), which would therefore be relatively unresponsive to the differentiating effect of KGF. Taken together, using a human primary culture model, we have demonstrated key roles for interactions between KGF and integrin-mediated function in the regulation of prostate epithelial differentiation.

Androgens modulate the inflammatory response during acute wound healing

Impaired wound healing states in the elderly lead to substantial morbidity and mortality, and a cost to the health services of over 9 billion dollars per annum. In addition to intrinsic ageing processes that per se cause delayed healing, studies have suggested marked differences in wound repair between the sexes. We have previously reported that, castration of male mice results in a striking acceleration of local cutaneous wound healing and dampens the associated inflammatory response. In this study, we report that systemic 5alpha-reductase inhibition, which blocks the conversion of testosterone to its more active metabolite 5alpha-dihydrotestosterone, mimics the effects of castration in a rat model of cutaneous wound healing. The mechanisms underlying the observed effects involve a direct, cell-specific upregulation of pro-inflammatory cytokine expression by macrophages, but not fibroblasts, in response to androgens. Androgens require the transforming growth factor beta signalling intermediate Smad3 to be present in order to influence repair and local pro-inflammatory cytokine levels. That reducing 5alpha-dihydrotestosterone levels through 5alpha-reductase antagonism markedly accelerates healing suggests a specific target for future therapeutic intervention in impaired wound healing states in elderly males.

Ca2+ currents in smooth muscle cells isolated from human prostate

BACKGROUND

The objective of the investigation was to demonstrate the presence of voltage-dependent Ca2+ current in human prostate smooth muscle cells and to determine their biophysical characteristics.

METHODS

Prostate smooth muscle cells were isolated from biopsy samples of human prostates obtained from prostatectomy specimens or TURP chips. Electrophysiological recordings were made under current- or voltage-clamp using patch-type electrodes.

RESULTS

The average resting potential of prostate myocytes was 63 +/- 11 mV and action potentials (APs) could be elicited when K+ currents were blocked. With K-filled electrodes inward current was followed by a large outward component. When K+ currents were blocked a large Ca2+-sensitive inward current was measured. The inward current could be divided into two components, a fraction blocked by 30 microM verapamil and another by 20 microM NiCl2.

CONCLUSIONS

Based on the sensitivity to antagonists and holding potential both L-type and T-type Ca2+ channels were identified in human prostate smooth muscle.

Relationship between upregulated oestrogen receptors and expression of growth factors in cultured, human, prostatic stromal cells exposed to estradiol or dihydrotestosterone

This study investigated the hypothesis that, in benign prostatic hyperplasia (BPH), upregulated oestrogen receptors (ER) and the action of androgens differentially regulate expression of stromal growth factors. Eight human prostatic stromal cell strains were subjected to a procedure to upregulate their ER by exposing them to 1 micromol 17beta-estradiol for 10 days followed by passage and growth in the absence of steroids. Four of the cell strains instead received 100 nmol dihydrotestosterone for 48 h. Immunoexpression of ERalpha, AR and six growth factors was quantified by flow cytometry in each case. Expression of ERalpha was significantly increased in six of eight cell strains. Expressions of six growth factors (FGF-2, FGF-7, IGF-1, TGF-beta1 NGF and e NOS) were elevated but only for FGF-7 was it significant. There was a significant positive correlation between the change in ERalpha and the change in FGF-2 and FGF-7, but not the other growth factors. Exposure to dihydrotestosterone reduced expression of ERalpha and all six growth factors, compared with oestrogen-treated cells but not significantly. It is concluded that upregulated ERalpha in prostatic stroma may have a greater modulating influence on synthesis of certain growth factors than the direct action of androgens and, by enhancing synthesis of FGF-2 and FGF-7, could play a significant role in the development of BPH.

Pharmacological inhibition of FGF receptor signaling inhibits LNCaP prostate tumor growth, promatrilysin, and PSA expression

Previously we have shown that the matrix metalloproteinase matrilysin (MMP-7) is overexpressed in human prostate cancers compared with normal epithelium. However, the mechanism for this overexpression is not understood. Human prostate fibroblasts have been shown to express certain fibroblast growth factors (FGFs), including FGF-1. Evidence from our laboratory and others has indicated that FGFs can regulate the expression of certain matrix metalloproteinases, including matrilysin. The goal of this study was to determine whether pharmacological inhibition of FGFR signaling would alter LNCaP tumor growth as well as expression of promatrilysin when LNCaP cells were co-injected subcutaneously with human prostate fibroblasts into athymic nude mice. For these inhibitor studies, AG1-X2 beads were coated with the pharmacological FGFR inhibitor SU5402 and were co-injected along with LNCaP and human prostate fibroblast cells (PF). Mice injected with LNCaP/PF and LNCaP/PF/beads alone demonstrated significant tumor growth, whereas mice injected with LNCaP/PF/SU5402-coated beads showed a significant decrease in tumor volume and weight. Immunohistochemical analysis showed that significant promatrilysin expression in tumors was inhibited by the FGFR inhibitor SU5402. Serum prostate-specific antigen (PSA) and promatrilysin levels were measured by enzyme-linked immunosorbent assay. The mice injected with LNCaP/PF and LNCaP/PF/beads expressed promatrilysin and serum PSA levels that were inhibited by co-injecting with SU5402. Therefore, pharmacological inhibition of FGF receptor signaling results in a decrease in the growth of LNCaP tumors generated subcutaneously by co-injecting LNCaP cells and human prostate fibroblasts. The inhibition in tumor growth was correlated with a decrease in tumor promatrilysin expression and a decrease in serum promatrilysin and PSA.

Fibroblast growth factors and their receptors in urological cancers: basic research and clinical implications

Because therapeutical options for advanced urological cancers are limited, the understanding of key elements responsible for invasion and metastasis is very important. It has been hypothesized that progression to malignant growth is associated with a dysregulation of growth factors and/or their receptors. In the last few years, signaling pathways of the fibroblast growth factor (FGF) family have been subject to intense investigation. Fibroblast growth factors constitute one of the largest families of growth and differentiation factors for cells of mesodermal and neuroectodermal origin. The family comprises two prototypic members, acidic FGF (aFGF) and the basic FGF (bFGF), as well as 21 additionally related polypeptide growth factors that have been identified to date. FGFs are involved in many biological processes during embryonic development, wound healing, hematopoesis, and angiogenesis. In prostate, bladder, and renal cancers, FGFs regulate the induction of metalloproteinases (MMP) that degrade extracellular matrix proteins, thus facilitating tumor metastasis. Probably due to their potent angiogenic properties, aFGF and bFGF have received the most attention. However, there is increasing evidence that other FGFs also play crucial roles in tumors of the prostate, bladder, kidney, and testis. This review will discuss the different elements involved in FGF signaling and summarize the present knowledge of their biological and clinical relevance in urological cancers.

Modulation of androgen receptor protein by culture conditions of human skin fibroblasts

Cultures of skin fibroblasts show variation of androgen binding with culture conditions; binding variations are usually avoided by using confluent cultures. In this work, we analysed the effect of cell density and mitogenic agents on the level of androgen receptor (AR) of cultured human skin fibroblasts. Results demonstrated that in cultures of human skin fibroblasts, cellular binding of dihydrotestosterone was higher in cells grown at low than at high cell density. The reduction in binding resulted from a decrease in the number of high affinity receptors and not from a change in receptor affinity. Immunocytochemistry for AR showed greater staining intensity in cells grown at low than at high cell density. Additionally, immunoblot analysis demonstrated more AR protein in low cell density cultures. On the other hand, it was observed that cells grown at low cell density showed diminished androgen binding capacity after 24 h of treatment with insulin-like growth factor (IGF-l), basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), or granulocyte-colony stimulating factor (G-CSF); this effect of growth factors was not observed in cells grown at high cell density. In conclusion, we found that cell density of cultures and mitogenic agents can regulate AR binding activity in human fibroblasts. While we do not yet know how changes in cell density affect the amount of AR, we conclude that the mechanism could be mediated by activation of the tyrosine kinase pathway, as the effect was reproduced by mitogens.