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Regulation of Iron Homeostasis through Parkin-Mediated Lactoferrin Ubiquitylation
journal contribution
posted on 2020-08-06, 22:22 authored by Ankur
A. Gholkar, Stefan Schmollinger, Erick F. Velasquez, Yu-Chen Lo, Whitaker Cohn, Joseph Capri, Harish Dharmarajan, William J. Deardorff, Lucy W. Gao, Mai Abdusamad, Julian P. Whitelegge, Jorge Z. TorresSomatic mutations
that perturb Parkin ubiquitin ligase activity
and the misregulation of iron homeostasis have both been linked to
Parkinson’s disease. Lactotransferrin (LTF) is a member of
the family of transferrin iron binding proteins that regulate iron
homeostasis, and increased levels of LTF and its receptor have been
observed in neurodegenerative disorders like Parkinson’s disease.
Here, we report that Parkin binds to LTF and ubiquitylates LTF to
influence iron homeostasis. Parkin-dependent ubiquitylation of LTF
occurred most often on lysines (K) 182 and 649. Substitution of K182
or K649 with alanine (K182A or K649A, respectively) led to a decrease
in the level of LTF ubiquitylation, and substitution at both sites
led to a major decrease in the level of LTF ubiquitylation. Importantly,
Parkin-mediated ubiquitylation of LTF was critical for regulating
intracellular iron levels as overexpression of LTF ubiquitylation
site point mutants (K649A or K182A/K649A) led to an increase in intracellular
iron levels measured by ICP-MS/MS. Consistently, RNAi-mediated depletion
of Parkin led to an increase in intracellular iron levels in contrast
to overexpression of Parkin that led to a decrease in intracellular
iron levels. Together, these results indicate that Parkin binds to
and ubiquitylates LTF to regulate intracellular iron levels. These
results expand our understanding of the cellular processes that are
perturbed when Parkin activity is disrupted and more broadly the mechanisms
that contribute to Parkinson’s disease.