Regulation of IκBβ Expression in Testis

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Abstract
IκBα and IκBβ are regulators of the nuclear factor-κB (NF-κB) transcription factor family. Both IκBs bind to the same NF-κB dimers and are widely expressed in different cells and tissues. To better understand how these two IκB isoforms differ biologically, we have characterized the expression of IκBβ in testis, a tissue in which IκBα is only minimally expressed. We have found that IκBβ expression is localized within the haploid spermatid stages of spermatogenesis and follows the expression of nuclear NF-κB. IκBβ expression in haploid spermatids is likely regulated by Sox family proteins, members of which are also expressed within spermatids. We have shown that both SRY and Sox-5 can bind to multiple Sox binding sites found within the IκBβ promoter and can enhance transcription of a reporter gene in transient transfection assays. We also demonstrate that IκBβ mRNA is strongly expressed in developing male gonads. These results therefore suggest that IκBβ may be a novel target for transcription factors of the HMG-box SRY/Sox family and imply a potential role for NF-κB/IκBβ in spermatogenesis.