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Positive Regulator Molecules

Positive Regulator Molecules

Mitotic cell division results in daughter cells that exactly resemble the parent cell. However, errors in the DNA replication or distribution of genetic material may lead to genetic mutations that may be passed down to every new cell formed from the resulting abnormal cell. Propagation of such mutant cells is restricted through checkpoint mechanisms present at different stages of the cell cycle. These checkpoints involve regulator molecules that either promote or demote cell cycle events.

Positive Regulator Molecules

Positive Regulator Molecules

To consistently produce healthy cells, the cell cycle—the process that generates daughter cells—must be precisely regulated.

Inhibition of Cdk Activity

Inhibition of Cdk Activity

The orderly progression of the cell cycle depends on the activation of Cdk protein by binding to its cyclin partner. However, the cell cycle must be restricted when undergoing abnormal changes. Most cancers correlate to the deregulated cell cycle, and since Cdks are a central component of the cell cycle, Cdk inhibitors are extensively studied to develop anticancer agents. For instance, cyclin D associates with several Cdks, such as Cdk 4/6, to form an active complex. The cyclin D-Cdk4/6 complex...

Anaphase Promoting Complex

Anaphase Promoting Complex

The stepwise destruction of specific proteins is necessary for the progression and completion of the cell cycle. Such proteins are ubiquitinated by ubiquitin ligases and then subsequently destroyed by the proteasome. The SCF (Skp1/Cullin/F-box) and the anaphase-promoting complex (APC) are two important ubiquitin ligases involved in cell cycle progression. While SCF is active throughout the cell cycle, APC gets activated during metaphase to anaphase transition. Cdc20 or Cdh1 binds to APC and...

Hormones of the Pituitary Gland

Hormones of the Pituitary Gland

The small, pea-sized pituitary gland is located at the base of the brain. It is crucial in regulating various bodily functions, from growth to reproduction. The gland is divided into the anterior lobe and the posterior lobe. The secretory cell clusters in the pars distalis of the anterior pituitary lobe are controlled by hypothalamic regulators and synthesize six primary hormones.
The most abundantly secreted hormone from the anterior lobe is the growth hormone, which controls overall growth by...

Negative Regulator Molecules

Negative Regulator Molecules

Positive regulators allow a cell to advance through cell cycle checkpoints. Negative regulators have an equally important role as they terminate a cell’s progression through the cell cycle—or pause it—until the cell meets specific criteria.

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Related Experiment Video

Updated: Dec 16, 2025

Endoscopic Endonasal Trans-sphenoidal Approach: Minimally Invasive Surgery for Pituitary Adenomas

Endoscopic Endonasal Trans-sphenoidal Approach: Minimally Invasive Surgery for Pituitary Adenomas

Published on: January 17, 2018

Cyclin A in nonfunctioning pituitary adenomas.

Elisa B Lamback¹, Alexandro Guterres², Monique Alvares Barbosa³

¹Neuroendocrinology Research Center/ Endocrinology Division, Medical School and Hospital Universitário Clementino Fraga Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.

|July 5, 2020

Summary

Cyclin A is elevated in a small fraction of nonfunctioning pituitary adenomas (NFPA). This study found no association between cyclin A expression and tumor invasion or proliferation, suggesting it may not predict recurrence risk.

Keywords:

Cyclin A Invasion Nonfunctioning pituitary adenomas Proliferation Tumorigenesis

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Last Updated: Dec 16, 2025

Endoscopic Endonasal Trans-sphenoidal Approach: Minimally Invasive Surgery for Pituitary Adenomas

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Published on: January 17, 2018

Identification of Cyclin-dependent Kinase 1 Specific Phosphorylation Sites by an In Vitro Kinase Assay

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Published on: May 3, 2018

Studying Proteolysis of Cyclin B at the Single Cell Level in Whole Cell Populations

Studying Proteolysis of Cyclin B at the Single Cell Level in Whole Cell Populations

Published on: September 17, 2012

Area of Science:

Endocrinology
Oncology
Molecular Biology

Background:

Nonfunctioning pituitary adenomas (NFPA) represent a significant portion of pituitary tumors.
Tumor invasion and proliferation are key indicators of recurrence risk in NFPA.
Understanding molecular markers associated with tumor behavior is crucial for patient management.

Purpose of the Study:

To assess the expression of cyclin A in NFPA.
To compare cyclin A expression between non-invasive, non-proliferative tumors and invasive, proliferative tumors.
To determine if cyclin A correlates with tumor aggressiveness and recurrence risk.

Main Methods:

Quantitative real-time polymerase chain reaction (qRT-PCR) was used to analyze cyclin A expression.
Normal pituitary gland tissue served as the reference for fold change (FC) calculations.
Tumor invasion was assessed using the Knosp criteria, and proliferation was determined by Ki-67 index, mitotic count, and p53 expression.

Main Results:

Cyclin A expression was analyzed in 31 NFPA patients, with a median FC of 0.31.
No significant difference in cyclin A expression was found between non-invasive/non-proliferative and invasive/proliferative tumors (p=0.968).
Elevated cyclin A (FC > 1.0) was observed in 12.9% of tumors, irrespective of invasion or proliferation status.

Conclusions:

Cyclin A is elevated in a minority of nonfunctioning pituitary adenomas.
Cyclin A expression does not appear to be related to tumor invasion or proliferation in NFPA.
Further research is needed to elucidate the role of cyclin A in pituitary tumorigenesis.