Immunohistochemical localization of activated Stat3 and hTERT protein in psoriasis vulgaris

ARTICLE

Immunohistochemical localization of activated Stat3 and hTERT protein in psoriasis vulgaris

Auteur(s) : Houjun LIU^1,2, Yoichi MOROI¹, Shinichiro YASUMOTO³, Hisashi KOKUBA¹, Shinichi IMAFUKU¹, Takeshi NAKAHARA¹, Teruki DAINICHI¹, Hiroshi UCHI¹, Yating TU², Masutaka FURUE¹, Kazunori URABE¹

¹ Department of Dermatology, Graduate School of Medical Sciences, Kyushu University, Maidashi 3-1-1, Higashiku, Fukuoka, 812-8582, Japan
² Department of Dermatology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology
³ Department of Dermatology, Kurume University
Fax: (+ 81)-92-642-5600,
<kaurabe@dermatol.med.kyushu-u.ac.jp>

Psoriasis is an inflammatory disease induced by autoreactive interferon (IFN)- producing T helper cell (Th) 1 lymphocytes which orchestrate other cellular reactions, resulting in hyperproliferation of keratinocytes, concomitant inflammation, and dermal proliferation of small vessels [1]. However, the underlying mechanism of increased keratinocyte growth remains controversial.
Signal transducer and activator of transcription-3(Stat3) is a cytoplasmic latent transcription factor that is activated by tyrosine phosphorylation by members of the Janus kinases (Jak) family in response to a variety of cytokines and growth factors. Stat3 modulates cell proliferation, apoptosis, differentiation, and many other important biological activities [2]. Lovato et al. showed that a constitutive activation of Stat3 in non-transformed human T cells from Crohn’s disease [3], which is as same as psoriasis with a dysregulation of the cytokine network with a dominance of Th1 cytokine (IFN-γ, TNF-α, IL-12) and a deficiency in Th2 cytokines (IL-4 and IL-10). Most of these cytokines/cytokine receptors transduce signals through the Jak/STAT signaling pathways [2]. Moreover, an overexpression of cyclin D, Bcl-xL and VEGF, the downstream of Stat3, was present in psoriasis vulgaris. So, activated Stat3 signaling might be involved in the pathogenesis of psoriasis vulgaris.
Telomerase is a specialized reverse transcriptase that maintains the length of telomeres by adding repeat units to the telomere end. It is a ribonucleoprotein complex comprised of two core subunits, a template RNA subunit [human telomerase RNA (hTR)] and a catalytic protein subunit [human telomerase reverse transcriptase (hTERT)] [4], important for telomere maintenance and stability. Many findings strongly suggest that hTERT is the rate-limiting determinant of enzymatic activity of human telomerase [4]. Consequently, hTERT expression is used as a surrogate for telomerase activity. It has been suggested that telomerase activity is a biomarker of cell proliferation, not of malignant transformation [5]. Because there is apparent hyperproliferation of keratinocytes and dermal proliferation of small vessels in psoriasis, hTERT overexpression might exist.
To gain insight into the role of p-Stat3 and hTERT on the proliferation of keratinocytes and to further investigate the pathogenesis of psoriasis vulgaris, we examined immunohistochemically the expression of hTERT and p-Stat3 protein in psoriatic skin.
A total of 22 tissue specimens of psoriasis vulgaris and two circumcised normal foreskins were examined in this study. The study group comprised 12 male and 10 female patients, with a mean age of 36 years (range, 21 to 58 years). The paraffin- embedded tissue was evaluated with hematoxylin and eosin staining to confirm the diagnoses. Immunostaining was performed with antibodies against p-Stat3 (Cell signaling technology, Beverly, USA) and hTERT (NCL- hTERT, Novo Castra, Newcastle, UK) by biotin-avidin method.
Semi-quantitative assessment of the expression was performed according to the following criteria: –; < 5% cells were positive; +, 5-25% cells were positive; 2 +, 26-50% cells were positive, and 3 +, > 51% cells were positive. Histological images were captured from the microscope at an objective magnification of x 40, in 5-10 randomly chosen fields, from basal to granular layer.
Nineteen of 22 specimens were positive for p-Stat3 staining. Among 19 positive specimens, 5 specimens were positive for > 50% cells, 10 specimens were positive for 26-50% cells and 4 specimens were positive for 5-25% cells. The staining pattern was in the nuclei of the epidermal cells except the cornified layer (figure 1A) and in some vascular endothelial cells (figure 1B).
Eighteen of 22 specimens were positive for hTERT staining. Among 18 positive specimens, 5 specimens were positive for > 51% cells, 8 specimens were positive for 26-50% cells and 5 specimens were positive for 5-25% cells. The staining for hTERT was found in the nuclei of the epidermal cells except the cornified layer figure 1C), and more intensely in the nucleoli of cells figure 1D).
Psoriasis vulgaris is a chronic skin disease characterized by excessive but controlled keratinocyte proliferation and accumulation of numerous inflammatory mediators in the involved areas. Bowcock et al. recently demonstrated by gene microarray assay that there is an increase in the expression levels of the Stat3 gene in psoriasis vulgaris [6]. In the present study, nineteen specimens were positive in the epidermis and the vascular endothelial cells for the p-Stat3 protein, suggesting that the Stat3 is activated in epidermis cells and vascular endothelial cells of psoriasis vulgaris. Although Stat3 was proposed to be an oncogene [2], naturally occurring mutations of Stat3 that lead to its constitutive activation have not been identified. It is therefore proposed that aberrant growth factor signaling may play an important role in the constitutive activation of Stat3 [2]. In psoriasis, many cytokines (e.g. IL-6, IL-20) and growth factor (e.g. EGF, VEGF), which can activate Stat3, are overexpressed. Moreover, an overexpression of cyclin D, Bcl-xL and VEGF, the Stat3 target genes, was present in psoriasis vulgaris. So, activated Stat3 signaling may participate in the pathogenesis of psoriasis by stimulating cell proliferation and preventing apoptosis.
Many studies have suggested that hTERT plays a key role in cellular aging, immortalization, and transformation [4]. In the present studies, staining for hTERT was found in the nuclei of epidermal cells, and more intensely in the nucleoli of cells in psoriasis, primarily in some proliferating keratinocytes. This indicates that telomerase activity does not always correlate with the malignant phenotype [5]. This finding, that staining for hTERT was observed in keratinocytes in the upper to middle layers of the epidermis, supports the concept that proliferating and nonproliferating cells can express human telomerase RNA (hTER). Therefore, it may be speculated that one possible mechanism of epidermis hyperplasia in psoriasis might be the increased telomerase activity in psoriatic epidermis.
We can conclude that activated Stat3 signaling may participate in the pathogenesis of psoriasis by stimulating cell proliferation and preventing apoptosis, and hTERT may be related to epidermis hyperplasia in psoriasis. n

References

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