The 27 kDa heat shock protein (hsp27) is expressed in keratinocytes in a differentiation-related pattern. Keratinocyte differentiation involves a coordinated program of expression and interaction of specific differentiation-related genes and proteins. To investigate the functional role of hsp27 in these processes we used a differential display approach to identify genes that might be regulated by the expression of hsp27 in human keratinocytes. mRNA was extracted from the human squamous carcinoma cell line A431 and a subclone stably transfected with human hsp27. Reverse transcriptase differential display polymerase chain reaction was performed using one base anchored oligo-dT and arbitrary primers. Differentially expressed genes were confirmed by northern blot analysis and further characterized by sequencing. Their expression in human skin and other tissues was investigated by northern blot and in situ hybridization. Out of five fragments detected with the initial reverse transcriptase differential display polymerase chain reaction screen one could be confirmed by northern blot to be downregulated in hsp27-overexpressing A431. This mRNA (G24) is not only downregulated by overexpression of hsp27 in A431 but also during differentiation in normal human keratinocytes in culture and in situ, situations where hsp27 is known to be induced. According to sequence analysis G24 represents a novel gene that does not code for a protein and thus might belong to the growing family of noncoding RNAs. These results not only demonstrate for the first time that overexpression of hsp27 by gene transfer is associated with regulation of gene expression but also reveal a novel differentiation-associated gene in human keratinocytes.