Biology subjects

Orofiamma, L. A.

Publications and source records attributed to Orofiamma, L. A..

3 recordsLinked to original sources

bioRxiv2025

AMPK Repositions Early Endosomes via Gapex-5 to Promote Delivery of Iron to Mitochondria

The regulation of the spatial organization of organelles within cells is critical for coordinating signaling, membrane traffic, and metabolite exchange. Metabolic cues regulate the position and function of lysosomes, yet whether and how metabolic signals may similarly regulate other organelles such as early endosomes (EEs) remains unclear. We find that AMP-activated protein kinase (AMPK), a key regulator of metabolic homeostasis activated in response to nutrient scarcity, triggers movement of EEs to the perinuclear region of cells, leading to enhanced proximity of endosomes to mitochondria and increased delivery of iron to mitochondria. The movement of EEs and increased mitochondrial iron content elicited by AMPK activation requires Gapex-5, a GEF for the early endosome Rab5 previously shown to be an AMPK substrate. These findings reveal a mechanism by which AMPK reprograms endosome positioning to facilitate inter-organelle communication and iron delivery to mitochondria to support metabolic adaptation under conditions of nutrient scarcity.

cell biology↗

bioRxiv2024

Cargo-selective regulation of clathrin-mediated endocytosis by AMP-activated protein kinase

The cell surface abundance of many proteins is controlled by clathrin-mediated endocytosis (CME). CME is driven by the assembly of clathrin and other proteins on the inner leaflet of the plasma membrane into clathrin-coated pits (CCPs). Regulation of CCP dynamics allows for control of the function of specific cell surface proteins, impacting a range of cellular outcomes. AMP-activated protein kinase (AMPK) becomes activated upon metabolic insufficiency and facilitates cellular adaptation to nutrient stress. Here, we examined how AMPK regulates CME and the cell surface membrane traffic of {beta}1-integrin. We find that AMPK controls CCP dynamics and regulates the abundance of the endocytic adaptor protein Dab2 within CCPs in a manner that requires the GTPase Arf6, thus selectively promoting the CCP recruitment and internalization of {beta}1-integrin. This reveals a novel signaling pathway for cargo-selective metabolic regulation of CME by AMPK, impacting the function of cell surface proteins such as integrins.

cell biology↗

bioRxiv2022

HER2 expression defines unique requirements for flotillin and c-Src for EGFR signaling

The epidermal growth factor receptor (EGFR) controls many cellular functions. Upon binding its ligand, the receptor undergoes dimerization, phosphorylation, and activation of signals including the phosphatidylinositol-3-kinase (PI3K)-Akt pathway. While some studies indicated that EGFR signaling may be controlled by signal enrichment within membrane raft nanodomains, others have found a limited effect of membrane raft disruption on EGFR signaling, suggesting that specific factor(s) may define context-specific control of EGFR signaling by membrane rafts. Ligand-bound EGFR can homodimerize, or instead undergo heterodimerization with the related receptor HER2 when the latter is expressed. We examined how EGFR signaling in the presence of HER2 distinctly requires membrane raft nanodomains. Induction of HER2 expression altered EGFR signaling duration consistent with EGFR/HER2 heterodimer formation. EGFR and c-Src localized within plasma membrane structures demarked by flotillin, a membrane raft protein, selectively in HER2-expressing cells. Consistently, HER2-expressing cells, but not cells lacking HER2, were dependent on flotillin and c-Src for EGFR signaling leading to Akt activation and cell proliferation. Hence, HER2 expression establishes the requirement of EGFR signaling for flotillin membrane rafts and c-Src, leading to Akt activation. Summary statementThe role of membrane rafts in EGFR signaling may be context-specific. We find that the related receptor HER2 defines unique signaling requirements for EGFR for membrane rafts, flotillin, and c-Src.

cell biology↗