Naslov
Transcriptional regulation of the cholesterol biosynthetic pathway in male germ cells

Autori
Fon Tacer, Klementina ; Kalanj-Bognar, Svjetlana ; Rozman, Damjana

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
5th Meeting of the Slovenian Biochemical Society with International Participation / Dolinar, Marko ; Križaj, Igor ; Turk, Vito - Ljubljana : Slovenian Biochemical Society, 2003

Skup
5th Meeting of the Slovenian Biochemical Society with International Participation

Mjesto i datum
Ljubljana, Slovenija, 24.09.2003. - 28.09.2003

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
cholesterol biosynthesis; transcriptional regulation; male germ cells

Sažetak
Expression of cholesterogenic genes in somatic cells generally follows cholesterol level-sensitive negative feedback loop. In contrast, expression of genes involved in cholesterol biosynthesis in male germ cells is insensitive to the negative cholesterol feedback regulation. The pathway is regulated at the level of transcription by transcription factors of the sterol regulatory element-binding protein (SREBP) family. It was proposed that SREBPs do not play a significant role in transcriptional regulation of cholesterol synthesis in male germ cells, in which the accumulation of cholesterol biosynthesis intermediates with signalling properties (sterols MAS) and predomination of the cAMP-dependent signalling cascade was clearly established. Male germ cells do not grow in a clean primary culture, which is a limiting factor in experimental approaches. We have thus developed an ex vivo system, with the aim to simulate the cholesterol biosynthesis conditions in the testis. The level of transcription factors SREBPs in human choriocarcinoma cell line JEG-3 was reduced by growing cells in cholesterol/fatty acid rich media. The trans-activation by the cAMP-dependent pathway was achieved by forskolin and overexpressing transcription factor CREB. The simulation was only partially successful. cAMP-stimulation in cholesterol-repressed conditions lead to a decrease in cholesterol quantity, which is in accordance with metabolism of male germ cells that are not efficient in producing cholesterol de novo. In contrary to expectations, activation of the cAMP-dependent pathway did not result in a change of sterol composition and quantity. The role of SREBPs in spermatogenic cells was a puzzle until recently, when a soluble, 55 kDa cholesterol-insensitive form of SREBP2 (SREBP2gc), translated from a germ cell-specific SREBP2 mRNA, was discovered (Wang H. et. al., Mol. Cell. Endo 22, 8478-8490, 2002), . Our RT-PCR results also showed that SREBP2 as well as SREBP1c mRNAs are detectable in prepubertal and post-pubertal male germ cells while SREBP1a is not detected. Surprisingly, three SREBP2 immunoreactive proteins (72, 63 and 55 kDa), that are not present in mouse liver nuclei, reside in testis nuclei of prepubertal and adult mice. The 55 kDa protein is likely SREBP2gc, the other two isoforms are novel. HPLC measurements in liver and testes of fasted prepubertal and post-pubertal mice showed no significant difference in cholesterol level. However, FF-MAS and lanosterol/T-MAS intermediates that are detectable mainly in testis increase in fasted post-pubertal mice which coincides well with the elevated level of 68 kDa SREBP2. Similar to SREBP2gc, the two novel SREBP2 immunoreactive proteins seem to be insensitive to the level of cholesterol. In conclusion, it seems possible that cholesterol-independent forms of SREBPs together with cAMP-dependent stimuli, contribute to accumulation of cholesterogenic intermediates, the signaling sterols MAS.

Izvorni jezik
Engleski

Znanstvena područja
Računarstvo

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