Journal of Andrology
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Published-Ahead-of-Print August 9, 2006, DOI:10.2164/jandrol.106.000976

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Functional characterization of male germ cell-specific CREM isoforms

Saskia Jaspers , Birgit Gellersen , Rita Kempf , Annemarie Samelecos , Martin Bergmann , and Klaus Steger *

* To whom correspondence should be addressed. E-mail: klaus.steger{at}chiru.med.uni-giessen.de.

Due to alternative promoter usage, splicing and translational initiation, expression of the cAMP-responsive element modulator (CREM) gene results in the production of functionally different CREM proteins with either activating or repressing potential on target gene expression. Recently, we demonstrated two novel isoforms (CREM-{vartheta}2-F-G-H-Ib and CREM-{vartheta}2-G-H-Ib) in various germ cell types during normal and impaired human spermatogenesis. In contrast to known isoforms, these exhibit a transactivation domain but lack a KID domain resulting in a disruption of the open reading frame. In the present study, we functionally analyzed these isoforms. Investigation of both in-vitro and in-vivo expressed proteins from human testis RNA suggests that a novel upstream open reading frame in exon {vartheta}2 is translated from isoform CREM-{vartheta}2-F-G-H-Ib giving rise to a full length protein. Furthermore, in both isoforms, usage of downstream ATGs for translation initiation could be observed. Sequence-specific DNA-binding of CREM isoforms was confirmed by electrophoretic mobility shift assays. Luciferase reporter gene assays in cells transfected with novel CREM cDNAs demonstrated that protein kinase A dependent stimulation was inhibited by coexpression of CREM-{vartheta}2-F-G-H-Ib but not of CREM-{vartheta}2-G-H-Ib.


Key words: Infertility • Spermatogenesis • Testis • CREM






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