E-Ras improves the efficiency of reprogramming by facilitating cell cycle progression through JNK-Sp1 pathway

Area of Science:

• Stem cell biology
• Molecular mechanisms of cell reprogramming
• Cell cycle regulation

Background:

• Protein extracts from mouse embryonic stem cells (mESC) can induce pluripotency in adult somatic cells.
• The efficiency of induced pluripotent stem (iPS) cell generation varies with the source of mESC extracts.
• Embryonic Ras (E-Ras) expression differs between mESC lines, correlating with reprogramming efficiency.

Purpose of the Study:

• To investigate the role of E-Ras in the reprogramming of somatic cells into iPS cells.
• To elucidate the molecular mechanisms by which E-Ras enhances reprogramming efficiency.

Main Methods:

• Overexpression of E-Ras in fibroblasts.
• Analysis of cell proliferation and cell cycle phase transitions (G1 to S).
• Luciferase reporter assays to study transcription factor binding (SP1) to cyclin promoters.
• Inhibition of signaling pathways (JNK, ERK, p38) to determine downstream effects.
• Assessment of iPS cell generation efficiency with and without E-Ras or JNK inhibition.

Main Results:

• E-Ras overexpression in fibroblasts increased cell proliferation by upregulating cyclins D and E, accelerating the G1 to S phase transition.
• SP1 was identified as a key transcription factor mediating the upregulation of cyclins D and E by E-Ras.
• E-Ras specifically activated the c-Jun N-terminal kinase (JNK) pathway, not ERK or p38.
• Inhibition of JNK blocked E-Ras-induced cell proliferation and SP1 activation.
• E-Ras transduction enhanced iPS cell generation efficiency, an effect abrogated by JNK inhibition.

Conclusions:

• E-Ras promotes somatic cell reprogramming by activating the JNK pathway.
• The E-Ras/JNK axis upregulates cyclins D and E via SP1, driving cell proliferation necessary for iPS cell generation.
• This pathway is a critical mechanism for both protein extract-mediated and factor-mediated iPS cell induction.