The 15 members of the kallikrein-related serine peptidase (KLK) family have 
diverse tissue-specific expression profiles and putative proteolytic functions. 
The kallikrein family is also emerging as a rich source of disease biomarkers 
with KLK3, commonly known as prostate-specific antigen, being the current serum 
biomarker for prostate cancer. The kallikrein locus is also notable because it 
is extraordinarily responsive to steroids and other hormones. Indeed, at least 
14 functional hormone response elements have been identified in the kallikrein 
locus. A more comprehensive understanding of the transcriptional regulation of 
kallikreins may help the field make more informed hypotheses about the 
physiological functions of kallikreins and their effectiveness as biomarkers. In 
this review, we describe the organization of the kallikrein locus and the 
structure of kallikrein genes and proteins. We also focus on the transcriptional 
regulation of kallikreins by androgens, progestins, glucocorticoids, 
mineralocorticoids, estrogens, and other hormones in animal models and human 
prostate, breast, and reproductive tract tissues. The interaction of the 
androgen receptor with androgen response elements in the promoter and enhancer 
of KLK2 and KLK3 is also summarized in detail. There is evidence that all 
kallikreins are regulated by multiple nuclear receptors. Yet, apart from KLK2 
and KLK3, it is not clear whether all kallikreins are direct transcriptional 
targets. Therefore, we argue that gaining more detailed information about the 
mechanisms that regulate kallikrein expression should be a priority of future 
studies and that the kallikrein locus will continue to be an important model in 
the era of genome-wide analyses.