The ERK Signaling Cascade Inhibits Gonadotropin-Stimulated Steroidogenesis.

The response of granulosa cells to Luteinizing Hormone (LH) and Follicle- Stimulating Hormone (FSH) is mediated mainly by cAMP/protein kinase A (PKA) signaling. Notably, the activity of the extracellular signal-regulated kinase (ERK) signaling cascade is elevated in response to these stimuli as well. We studied the involvement of the ERK cascade in LH- and FSH-induced steroidogenesis in two granulosa-derived cell lines, rLHR-4 and rFSHR-17, respectively.

Nonassembled human chorionic gonadotropin subunits and alphaalpha-homodimers use fast-track processing in the secretory pathway in contrast to alphabeta-heterodimers.

In multimeric glycoproteins, like glycoprotein hormones, mutual subunit interactions are required for correct folding, assembly, and transport in the secretory pathway. However, character and time course of these interactions need further elucidation. The influence of the glycoprotein hormone alpha-subunit (GPHalpha) on the folding of the human chorionic gonadotropin (hCG) beta-subunit (hCGbeta) in hCG alphabeta-heterodimers was investigated in [(35)S]Met/Cys-labeled JEG-3 cells.

Rapid maturation of glycoprotein hormone free alpha-subunit (GPHalpha) and GPHalpha alpha homodimers.

The dynamics of glycoprotein hormone alpha-subunit (GPHalpha) maturation and GPHalpha alpha homodimer formation were studied in presence (JEG-3 choriocarcinoma cells) and absence (HeLa cells) of hCGbeta. In both cases, the major initially occurring GPHalpha variant in [35S]Met/Cys-labeled cells carried two N-glycans (M(r app) = 22 kDa). Moreover, a mono-N-glycosylated in vivo association-incompetent GPHalpha variant (M(r app) = 18 kDa) was observed.

Time-dependent folding of immunological epitopes of the human chorionic gonadotropin beta-subunit.

We have explored the possibility to use 14 different monoclonal antibodies in order to follow the formation of the respective epitopes during the biosynthesis of hCG subunits and their association in JEG-3 choriocarcinoma cells using pulse (30s to 5 min)-chase (0-180 min) experiments. We found central cystine knot epitope structures (epitope beta1) to be formed immediately and simultaneously with epitopes on the protruding hCG-beta loops 1 and 3. We found also differences in the time-dependent folding of beta2 and beta4 epitopes, which are highly overlapping structures on the loops 1+3.