Human RTEL1 stabilizes long G-overhangs allowing telomerase-dependent over-extension

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• Telomere maintenance is vital for genomic stability and preventing cellular senescence.
• Accelerated telomere attrition characterizes premature aging syndromes like Dyskeratosis congenita (DC).
• Mutations in the human RTEL1 gene cause Hoyeraal-Hreidarsson syndrome (HHS), a severe DC form with short telomeres and telomere damage.

Purpose of the Study:

• To investigate the role of human RTEL1 (hRTEL1) in telomere maintenance in human primary and tumor cells.
• To elucidate the mechanism by which hRTEL1 influences telomere length and integrity.

Main Methods:

• Transient depletion of hRTEL1 in human cells.
• Analysis of telomere length, G-overhang content, and POT1 association.
• Assessment of telomerase activity and targeting.
• Overexpression of POT1 to evaluate its effect on telomere length and overhangs.

Main Results:

• hRTEL1 depletion caused rapid telomere shortening specifically in telomerase-positive cells with long telomeres.
• The effect of hRTEL1 on telomere length was telomerase-dependent but did not affect telomerase biogenesis or targeting.
• RTEL1 depletion decreased G-overhang content and POT1 association with telomeres, with minimal telomere uncapping.
• Overexpression of POT1 rescued telomere length but not G-overhangs, indicating G-overhang loss as the primary defect.

Conclusions:

• hRTEL1 is essential for maintaining long telomeres by preserving G-overhangs.
• Preserved G-overhangs facilitate POT1 binding and subsequent telomere elongation by telomerase.
• Loss of G-overhangs due to RTEL1 depletion is the primary cause of telomere shortening in specific cellular contexts.