SP1 and xeroderma pigmentosum: Moreover, it has been found that an histone deacetylase (HDAC) inhibitor, valproic acid, caused an increase in transcription of a DNA damage recognition gene, the xeroderma pigmentosum, complementation group C (XPC) via increasing binding of both CREB1 and SP1 transcription factors in both HTB4 and HTB9 UBUC-derived cell lines [36].