Small Molecule Screening Identifies HSP90 as a Modifier of RNA Foci in Myotonic Dystrophy Type 1

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• Myotonic dystrophy type 1 (DM1) is a genetic disorder caused by CTG repeat expansions in the DMPK gene.
• Expanded CUG repeats form nuclear RNA foci, but factors controlling DMPK expression and foci formation are largely unknown.

Purpose of the Study:

• To identify factors that regulate DMPK expression and CUGexp RNA foci in DM1.
• To investigate the role of heat shock protein 90 (HSP90) in DM1 pathogenesis.

Main Methods:

• Unbiased small molecule screen in DM1 skeletal muscle myoblast cell line.
• HSP90 inhibition, knockdown, and overexpression studies.
• Analysis of DMPK mRNA levels and RNA foci formation.
• Investigation of p-STAT3 signaling pathway.

Main Results:

• HSP90 was identified as a modifier of endogenous RNA foci in DM1 cells.
• HSP90 inhibition enhanced RNA foci and upregulated DMPK mRNA in undifferentiated myoblasts.
• p-STAT3 was identified as a downstream mediator of HSP90's effect on DMPK mRNA and RNA foci.
• HSP90 inhibition showed an opposite effect in differentiated cells, downregulating DMPK mRNA independently of p-STAT3.

Conclusions:

• HSP90 plays a significant role in regulating DMPK mRNA levels and RNA foci in DM1.
• p-STAT3 is a key mediator in the HSP90 pathway affecting DM1 pathology.
• These findings reveal novel therapeutic targets for DM1 intervention.