Abstract: 【Abstract】 Objective To determine the expression of silent information regulator 1 （Sirt1）, Sirt3 and hypoxia-inducible factor 1α （HIF-1α） in cutaneous squamous cell carcinoma （CSCC） tissues and cells, and to explore their role in the occurrence and development of CSCC. Methods From January 2019 to December 2020, 30 lesional skin tissues were obtained from patients with histopathologically confirmed poorly-, moderately- or well-differentiated CSCC, and 30 normal skin tissues were obtained from patients with non-cancerous diseases in Department of Dermatology, General Hospital of Ningxia Medical University. A CSCC cell line A431 and a human keratinocyte cell line HaCaT were cultured. Immunohistochemical study, Western blot analysis and real-time quantitative PCR （RT-PCR） were performed to determine the protein and mRNA expression of Sirt1, Sirt3 and HIF-1α in CSCC tissues of different grades of differentiation and normal skin tissues, cytochemical and immunofluorescence staining and RT-PCR were conducted to determine the protein and mRNA expression of Sirt1, Sirt3 and HIF-1α in A431 and HaCaT cells, respectively. Comparisons of measurement data among multiple groups were performed by using one-way analysis of variance, and comparisons between two groups by using t test. Results Immunohistochemical study showed that the expression level of Sirt3 （expressed as the average optical density） was 100 ± 12.12, 117.72 ± 26.23, 127.32 ± 24.45, 132.71 ± 31.61 in the normal skin tissues and well-, moderately- and poorly-differentiated CSCC tissues respectively, and there was a significant difference among these groups（F = 20.14, P < 0.001）; the expression of Sirt1 and HIF-1α increased in turn from the normal skin tissues to the well-, moderately- and poorly-differentiated CSCC tissues, and significantly differred in these groups （F = 174.50, 225.00, respectively, both P < 0.001）. As Western blot analysis revealed, the expression level of Sirt3 significantly differed among the normal skin tissues, well-, moderately- and poorly-differentiated CSCC tissues （expressed as relative gray value: 1.000 ± 0.132, 1.403 ± 0.411, 1.387 ± 0.393, 1.677 ± 0.683, respectively; F = 34.97, P < 0.001）, and so did the expression levels of Sirt1 and HIF-1α （F = 69.29, 199.90, respectively, both P < 0.00l）, with a gradually increasing trend in their expression levels from the the normal skin tissues to well-, moderately- and poorly-differentiated CSCC tissues. RT-PCR showed that the mRNA expression of Sirt3, Sirt1 and HIF-1α was sequentially increased from the normal skin tissues to well-, moderately- and poorly-differentiated CSCC tissues, and significant differences were observed among these groups （F = 113.00, 174.50, 50.33, respectively, all P < 0.001）. The protein expression levels of Sirt3, Sirt1 and HIF-1α were significantly higher in the A431 cells than in the HaCaT cells （t = 16.75, 18.34, 27.76, respectively, all P < 0.001）, and so were their mRNA expression levels （t = 14.22, 9.62, 16.86, respectively, all P < 0.001）. Conclusion Increased expression of Sirt3, Sirt1 and HIF-1α was observed in CSCC tissues and cells， which may promote the occurrence and development of CSCC.

Key words: Carcinoma, squamous cell, Cell line, tumor, Keratinocytes, Hypoxia-inducible factor 1, alpha subunit, Silent information regulators