Lactogen enhances Nb2 cell GTPase activity after 4 hours incubation

Area of Science:

• Cellular signaling
• Endocrinology
• Molecular biology

Background:

• The lactogen receptor is implicated in G protein association, despite lacking a typical 7-transmembrane domain.
• Previous research suggests a potential link between lactogen signaling and G proteins in Nb2 cells.

Purpose of the Study:

• To investigate the acute effects of lactogens on GTP binding and GTPase activity in Nb2 cell membranes.
• To determine if lactogen receptor activation influences G protein function in Nb2 cells.

Main Methods:

• Incubation of Nb2 cell membranes with ovine PRL (oPRL) to measure GTP binding and GTPase activity.
• Utilizing (35)S-GTP and α-(32)P-GTP for photoaffinity labeling to assess G protein binding.
• Measuring GTPase activity via the release of (32)Pi from γ-(32)P-GTP.

Main Results:

• Acute incubation of Nb2 cell membranes with oPRL did not alter GTP binding or GTPase activity.
• Prolonged incubation (4-7 hours) of Nb2 cells with lactogen led to a significant increase in membrane GTPase activity.
• Previous studies showed that 4-hour lactogen incubation increased G protein β subunit concentration and Gi ADP-ribosylation.

Conclusions:

• Lactogen signaling does not produce an immediate effect on G protein GTP binding or GTPase activity in Nb2 cell membranes.
• A delayed mechanism (at least 4 hours) is involved in lactogen-induced modulation of G proteins in Nb2 cells.
• These findings support a role for delayed lactogen modulation of G proteins, impacting cellular responses over time.