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Selective deficiency of guanine nucleotide-binding protein Go in two dopamine-resistant pituitary tumors
1Research Unit on Reproductive and Developmental Biology, Hôpital Ste-Justine, Montréal, Québec, Canada.
Abstract:
G proteins were quantitated by immunoblot in normal rat anterior pituitary, an estrone-induced pituitary adenoma, and in two transplantable pituitary tumors resistant to dopamine, 7315a and MtTW15. Antisera specific for the alpha o and beta subunits or the alpha i subunit of G proteins were tested with all preparations. While the alpha i and beta subunits were found to be present in variable concentrations in all preparations, the alpha o subunit was very low or undetectable in the transplantable tumors. These findings suggest that tumor resistance to the dopamine inhibitory actions on prolactin release and on tumor growth may be due to the deficiency of a Go protein.
Insights
Dopamine resistance in pituitary tumors may stem from a deficiency in the alpha o subunit of G proteins (Go protein). This protein is crucial for dopamine
Area of Science:
- Endocrinology
- Molecular Biology
- Oncology
Background:
- G proteins mediate cellular responses to hormones like dopamine.
- Pituitary tumors can develop resistance to dopamine's inhibitory effects on prolactin.
- The specific G protein subunits involved in this resistance are not fully understood.
Purpose of the Study:
- To investigate the role of G protein subunits in dopamine-resistant pituitary tumors.
- To compare G protein expression in normal pituitary tissue versus tumor models.
Main Methods:
- Quantification of G protein alpha o, alpha i, and beta subunits using immunoblotting.
- Analysis of normal rat anterior pituitary, an estrone-induced adenoma, and two dopamine-resistant transplantable tumors (7315a, MtTW15).
Main Results:
- Alpha i and beta G protein subunits were present in variable amounts across all samples.
- The alpha o G protein subunit was significantly reduced or undetectable in the dopamine-resistant transplantable tumors (7315a and MtTW15).
Conclusions:
- A deficiency in the alpha o subunit of G proteins (Go protein) may underlie tumor resistance to dopamine.
- This deficiency could explain the impaired dopamine inhibition of prolactin release and tumor growth in these models.