Akt Signaling Is Sustained by a CD44 Splice Isoform-Mediated Positive Feedback Loop

Area of Science:

• Oncology
• Molecular Biology
• Cancer Cell Signaling

Background:

• Tumor cells frequently utilize sustained Phosphatidylinositol 3-kinase/Protein kinase B (PI3K/Akt) signaling for survival and apoptosis evasion.
• Mechanisms sustaining PI3K/Akt signaling in cancers lacking direct mutations remain largely unknown.

Purpose of the Study:

• To elucidate the molecular mechanisms sustaining PI3K/Akt signaling in breast cancer cells.
• To identify novel pathways involved in cancer cell survival.

Main Methods:

• Investigated the role of splice isoform CD44s in regulating PI3K/Akt signaling.
• Utilized molecular biology techniques to study the interaction between CD44s, hyaluronan synthase HAS2, and the transcription factor FOXO1.
• Analyzed clinical breast cancer specimens to correlate CD44s and HAS2 expression.

Main Results:

• Discovered a positive feedback loop where CD44s promotes HAS2 expression, and hyaluronan stimulates CD44s-mediated Akt signaling.
• Identified FOXO1 as a repressor of HAS2, whose phosphorylation by Akt is maintained by the feedback loop.
• Found a positive correlation between CD44s and HAS2 expression in human breast cancer samples.

Conclusions:

• Established a novel splice isoform-dependent positive feedback mechanism that sustains PI3K/Akt signaling in breast cancer.
• This pathway is critical for tumor cell survival, offering potential therapeutic targets.
• Highlights the importance of PI3K/Akt signaling in nearly all cancer cell survival.