Human telomerase acts as a hTR-independent reverse transcriptase in mitochondria

Area of Science:

• Mitochondrial biology
• Molecular genetics
• Cellular biology

Background:

• Human telomerase reverse transcriptase (hTERT) is known to function in the nucleus, but its presence and role in mitochondria are poorly understood.
• Telomerase activity is crucial for maintaining telomere length, but its extranuclear functions are largely unexplored.

Purpose of the Study:

• To investigate the biology and function of human telomerase reverse transcriptase (hTERT) within mitochondria.
• To determine if mitochondrial hTERT activity is dependent on the nuclear telomerase RNA (hTR).
• To elucidate the distinct cellular roles of nuclear versus mitochondrial telomerase.

Main Methods:

• Co-purification of mammalian TERT with mitochondrial nucleoids and tRNAs.
• RNA immunoprecipitation (RIP) assays in whole cells and in organello.
• In vitro reverse transcriptase assays using TERT and mitochondrial RNAs.
• Mitochondrial-specific depletion of hTERT while maintaining nuclear function.

Main Results:

• Mammalian TERT was found to be localized in mitochondria, associated with mitochondrial nucleoids and tRNAs.
• The canonical nuclear RNA component, human telomerase RNA (hTR), was not detected in mitochondria and is not required for mitochondrial telomerase effects.
• hTERT was shown to bind various mitochondrial RNAs, indicating reconstitution of reverse transcriptase activity with these RNAs.
• In vitro assays confirmed TERT's ability to synthesize cDNA independently of hTR.
• Specific absence of mitochondrial hTERT impaired mitochondrial function, distinct from its nuclear role.

Conclusions:

• Mitochondrial hTERT acts as a reverse transcriptase independently of hTR, utilizing mitochondrial RNAs.
• Nuclear and mitochondrial telomerases possess different cellular functions.
• These findings have significant implications for understanding mitochondrial biology and telomerase function.