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Pit-1 messenger ribonucleic acid is differentially expressed in human pituitary adenomas
K E Friend1, Y K Chiou, E R Laws
1Department of Internal Medicine, University of Virginia Health Sciences Center, Charlottesville 22908.
Abstract:
Thirty-four human pituitary adenomas were examined for the presence of Pit-1 mRNA via Northern analysis. All tumors that were immunoreactive with either human (h) PRL or hGH antiserum contained Pit-1 mRNA (8 of 8) as did a small percentage of alpha-subunit only (1 of 3) and null tumors (1 of 9). Two tumors that contained TSH beta mRNA by RNAse protection assay also contained Pit-1 mRNA. Tumors that were immunoreactive with antiserum for hACTH, hFSH beta, or hLH beta without containing PRL, GH, or TSH beta were uniformly Pit-1 negative (0 of 14). Although RNA from the majority of Pit-1-positive tumors (10 of 11) contained primarily a 2.4-kilobase (kb) Pit-1 mRNA transcript, 1 tumor appeared to contain a 1.6-kb mRNA. Analysis of human pituitary autopsy specimens revealed no 1.6-kb Pit-1 mRNA, indicating that this variant may be tumor specific. The wide variety of serum PRL, GH, and insulin-like growth factor-I levels in patients with Pit-1-positive tumors suggests that although Pit-1 is necessary for PRL and GH production, it is not uniformly associated with hormone production, as determined by either immunohistochemistry or elevated serum levels. The expression of Pit-1 mRNA in a small fraction of null and alpha-subunit only tumors indicates that there may be a previously unsuspected diversity of origin within these particular subsets of adenomas.
Insights
Pituitary tumors producing prolactin or growth hormone consistently contain Pit-1 mRNA. However, Pit-1 expression in other adenoma types suggests diverse origins and complex hormone regulation.
Area of Science:
- Endocrinology
- Molecular Biology
- Oncology
Background:
- Pit-1 is a transcription factor crucial for the development of specific anterior pituitary cell types.
- Pituitary adenomas are common tumors arising from the anterior pituitary gland.
- Understanding the molecular basis of pituitary adenomas is key to diagnosing and treating these conditions.
Purpose of the Study:
- To investigate the presence and significance of Pit-1 mRNA in various human pituitary adenomas.
- To explore the relationship between Pit-1 expression and hormone production in pituitary tumors.
- To identify potential tumor-specific variants of Pit-1 mRNA.
Main Methods:
- Northern blot analysis was used to detect Pit-1 mRNA in 34 human pituitary adenomas.
- Immunohistochemistry was employed to assess hormone and subunit expression (PRL, GH, alpha-subunit, TSH beta, ACTH, FSH beta, LH beta).
- RNAse protection assay was utilized for TSH beta mRNA detection.
Main Results:
- Pit-1 mRNA was detected in all tumors expressing prolactin (PRL) or growth hormone (GH).
- A small percentage of alpha-subunit only and null tumors also expressed Pit-1 mRNA.
- Tumors expressing ACTH, FSH beta, or LH beta without PRL, GH, or TSH beta were uniformly Pit-1 negative.
- A potential tumor-specific 1.6-kb Pit-1 mRNA variant was observed, distinct from the predominant 2.4-kb transcript found in normal pituitary tissue.
- Pit-1 positivity did not uniformly correlate with serum hormone levels, indicating complex regulatory mechanisms.
Conclusions:
- Pit-1 expression is strongly associated with PRL and GH-producing pituitary adenomas.
- The presence of Pit-1 mRNA in null and alpha-subunit tumors suggests a broader role and potential for diverse origins in these adenoma subtypes.
- A tumor-specific variant of Pit-1 mRNA may exist, warranting further investigation into its functional implications.