# Project 1: Determine the mechanisms Cyclin D-Cdk4/6 uses to drive cell proliferation

> **NIH NIH P01** · STANFORD UNIVERSITY · 2023 · $66,725

## Abstract

PROJECT SUMMARY
Human cell division is regulated at the G1/S transition before DNA is replicated. The primary drivers of cells
through the G1/S transition are the cyclin-dependent kinases Cdk4 and Cdk6 in complex with D-type cyclins.
The goal of this project is to determine the mechanisms that Cyclin D-Cdk4/6 complexes use to drive cell division.
This is important for cancer because Cdk4/6 activity is elevated in many cancers including breast cancers, brain
cancers, acute lymphoblastic leukemia, and neuroblastoma tumors. Inhibiting Cyclin D-Cdk4/6 is therefore a
promising avenue for therapies targeting these cancers. Here, we propose to determine how Cyclin D-Cdk4/6
drives the G1/S transition. First, we will do this by identifying all the targets of Cyclin D-Cdk4/6 kinases in cells
using a chemical genetic approach. Second, we will determine the molecular mechanism Cyclin D-Cdk4/6 uses
to dock and phosphorylate its primary target, the retinoblastoma protein Rb. In preliminary data, we discovered
that Cyclin D binds an alpha helix at the C-terminus of Rb. We now aim to determine the location on Cyclin D
that docks Rb’s C-terminal helix using a combination of in vitro biochemistry and structural biology approaches.
We propose to use knowledge of this docking interaction to develop a tool compound that disrupts the interaction
and arrests the cell cycle. This will allow testing of the importance of the interactions in cells and provides a
proof-of-principle that disrupting this interaction could be used in targeted cancer therapeutics. We will pursue
two directions to identify a tool compound. First, we will develop a peptide inhibitor based on Rb’s C-terminal
helix. Second, we will screen a small molecule library using a FRET assay. Taken together, the proposed
experiments will provide an in-depth analysis of the Cyclin D-Rb interaction and will determine how it drives cell
division. The broader impact of this study of the Cyclin D molecular docking mechanism and identification of
Cyclin D-Cdk4/6 substrates may be the identification of new small molecules that improve cancer therapy.

## Key facts

- **NIH application ID:** 10867552
- **Project number:** 3P01CA254867-02S1
- **Recipient organization:** STANFORD UNIVERSITY
- **Principal Investigator:** Jan M Skotheim
- **Activity code:** P01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2023
- **Award amount:** $66,725
- **Award type:** 3
- **Project period:** 2023-07-01 → 2026-02-28

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10867552

## Citation

> US National Institutes of Health, RePORTER application 10867552, Project 1: Determine the mechanisms Cyclin D-Cdk4/6 uses to drive cell proliferation (3P01CA254867-02S1). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10867552. Licensed CC0.

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