Regulation of the expression and activity by progestins of a member of the SOX gene family of transcriptional modulators J D Graham, S M N Hunt, N Tran and C L Clarke Westmead Institute for Cancer Research, University of Sydney, Westmead Hospital, Westmead, New South Wales 2145, Australia (Requests for offprints should be addressed to C Clarke, Department of Medical Oncology, Westmead Hospital, Westmead, New South Wales 2145, Australia) (J D Graham is now at Department of Medicine, University of Colorado Health Sciences Centre, 4200 E. 9th Avenue, Campus Box B151, Denver, Colorado, USA) ABSTRACT The mammalian testis-determining gene Sry and the related Sox genes define a family of transcrip- tional regulators widely expressed during embryo- genesis. Tightly controlled temporal profiles of expression are a feature of the Sox gene family and may be required for initiation of a cascade of gene expression, yet the molecular mechanisms that control Sox gene expression are unknown. We now show that human SOX4 is expressed in the normal breast and in breast cancer cells. In these cells SOX4 is a progesterone-regulated gene, the expression of which is increased by progestins, leading to a marked increase in SOX-mediated transcriptional activity. Treatment of T-47D breast cancer cells with the synthetic progestin ORG 2058 directly increased SOX4 transcription, resulting in a 4-fold increase in SOX4 mRNA levels within 4 h of treatment. No effect of ORG 2058 was noted on other SOX genes measured, nor were other hormone-regulated HMG box proteins detected in this system, suggesting that the observed ability of progestin to increase SOX mRNA expression was confined to SOX4. The increase in SOX4 transcrip- tion was reflected in increased SOX4 protein expression, as progestin treatment of T-47D cells transfected with a SOX-responsive reporter resulted in a marked increase in reporter gene expression. Progesterone is essential for normal development and differentiation of the female reproductive system, plays an essential role in regulating growth and differentiation of the mam- mary gland and is required for opposing the proliferative effects of estrogen in specific cell types. The detection of SOX4 expression in the normal and malignant breast and the demonstration that SOX4 expression is under progesterone control suggests that changes in SOX4 gene expression may play a role in commitment to the differentiated phenotype in the normal and malignant mammary gland. Journal of Molecular Endocrinology (1999) 22, 295–304 INTRODUCTION The SOX4 gene is a member of a family of transcription regulators which all contain an HMG box DNA-binding domain, and interact with DNA in a sequence-specific fashion (Pevny & Lovell-Badge 1997). Many SRY-related HMG box (SOX) genes have now been identified in the human, as well as other species, on the basis of their homology in this region. Where analysed, all have been shown to bind specifically to the double- stranded DNA motif, A/TA/TCAAA/TG (Denny et al. 1992, van de Wetering & Clevers 1992, Laudet et al. 1993, van de Wetering et al. 1993, Connor et al. 1995, Hosking et al. 1995). Interaction of HMG box proteins with this motif results in bending of the DNA, suggesting that transacti- vation by these factors may occur by facilitating protein–protein or protein–DNA interactions, bringing normally distal components into proximity with each other (Ferrari et al. 1992). Although it is still not possible to ascribe functions to all members of the Sox gene family, there is increasing evidence that Sox proteins are likely to be involved in many 295 Journal of Molecular Endocrinology (1999) 22, 295–304 0952–5041/99/022–295  1999 Society for Endocrinology Printed in Great Britain Online version via http://www.endocrinology.org Downloaded from Bioscientifica.com at 02/18/2023 08:18:34AM via free access