ORIGINAL ARTICLE

Expression and heterodimer-binding activity of Ku70 and Ku80 in human non-melanoma skin cancer

P Parrella¹, P Mazzarelli^2,*, E Signori^2,5, G Perrone⁴, G F Marangi³, C Rabitti⁴, M Delfino⁶, M Prencipe¹, A P Gallo¹, M Rinaldi⁵, G Fabbrocini⁶, S Delfino³, P Persichetti³ and V M Fazio^1,2

¹ Oncology Research Laboratory, IRCCS Hospital "Casa Sollievo della Sofferenza", San Giovanni Rotondo (FG), Italy
² CIR, Section for Molecular Medicine and Biotechnology, Campus Bio-Medico University, Rome, Italy
³ Division of Plastic and Reconstructive Surgery, Campus Bio-Medico University, Rome, Italy
⁴ Laboratory of Hystopathology, Campus Bio-Medico University, Rome, Italy
⁵ CNR INMM, Laboratory of Gene Medicine, Area of Rome "Tar Vergata", Rome, Italy
⁶ Department of Dermatology, University Federico II, Naples, Italy

Correspondence to:
Correspondence to:
V M Fazio
CIR, Section for Molecular Medicine and Biotechnology, Università Campus Bio-Medico, Via E Longoni 83, 00155 Rome, Italy; Fazio{at}unicampus.it

Background: Experimental data suggest that exposure to ultraviolet radiation may indirectly induce DNA double-strand breaks.

Aim: To investigate the contribution of the non-homologous end-joining repair pathway in basal and squamous cell carcinomas.

Methods: Levels of Ku70 and Ku80 proteins were determined by immunohistochemical analysis and Ku70–Ku80 heterodimer-binding activity by electrophoretic mobility shift assay. Matched pathological normal margins and skin from healthy people were used as controls.

Results: A significant increase in Ku70 and Ku80 protein levels was found for both tumour types as compared with normal skin (p<0.001). Squamous cell carcinoma showed increased immunostaining as compared with basal cell tumours (p<0.02). A direct correlation was found between Ku70 and Ku80 protein levels and expression of the proliferation markers Ki-67/MIB-1 (p<0.02 and p<0.002, respectively) in basal cell carcinoma. DNA binding activity was increased in basal cell carcinoma samples as compared with matched skin histopathologically negative for cancer (p<0.006). In squamous cell carcinomas, however, the difference was significant only with normal skin (p<0.02) and not with matched pathologically normal margins.

Conclusions: Overall, an up regulation of the Ku70 and Ku80 protein levels seems to correlate only with tumour proliferation rate. As non-homologous end joining is an error-prone mechanism, its up regulation may ultimately increase genomic instability, contributing to tumour progression.

Abbreviations: BCC, basal cell carcinoma; DSB, double-strand break; EMSA, electrophoretic mobility shift assay; IHC, immunohistochemical; NHEJ, non-homologous end joining; NMSC, non-melanoma skin cancer; SCC, squamous cell carcinoma; TBS, TRIS-buffered saline

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