<p>Signal transductions
are essential processes for living cells to react to environmental stimuli
adequately, and they need to be tightly regulated as they can affect cell
survival and cell fate determination. Since many of these signaling events rely
on the presence of receptors on the cell membrane, members of endocytic
proteins play critical regulatory roles in signaling via changing the
localization of the receptors. In particular, endocytic adaptors are the linkers that connect membrane cargo and other members of
endocytic machinery to accomplish the
process. We focused on the roles of the endocytic adaptors epsins and their
cargoes in signaling, as both epsins’ transmembrane and cytosolic cargoes
participate in signaling pathways.</p>
<p>We investigated
the molecular mechanism of how epsins recognize specific
ubiquitinated membrane cargoes among other ubiquitinated membrane
proteins. Through genetic, biochemical, and cell biological approaches, we identified the first yeast transmembrane
cargo, Ena1, a P-type ATPase sodium pump. We report that the simultaneous presence of phosphorylation
and ubiquitination on the Ena1
are required for epsin-specific recognition. We also demonstrated that post-translational modifications are Yck1/2
and Art3-Rsp5 dependent, and the spatial arrangement of the modifications is essential.
</p>
<p>In addition to the regulation
of signaling pathways through internalizing
transmembrane cargoes, epsins
are also involved in the regulation of
Rho GTPase signaling
pathways. Through direct interaction,
epsins inhibit activities of their cytosolic cargoes, Rho GTPase activating
proteins (RhoGAPs). Ocrl1 is one of the epsin interacting RhoGAP domain-containing
proteins. The deficiency of Ocrl1
leads to a lethal developmental disease
called Lowe syndrome (LS).
While the patients display developmental problems affecting the brain and eyes,
they also suffer from kidney dysfunction that results in death. The
pathological mechanism is currently obscure and no cure, partly due to the lack of an adequate cell model from the
affected tissues. We generated the first iPSC model from fibroblasts of LS
patients and normal individuals and further generated kidney cells from
these iPSCs. Consistent with observations obtained from LS fibroblasts,
the LS iPSC derived kidney
cells from patient cells also have a deficiency in
ciliogenesis.</p>
Further, we discovered that
Six2, a crucial transcriptional factor in kidney development, is mislocalized
to the Golgi-apparatus in patient iPSC-derived kidney cells as well as in an <i>OC</i><i>RL1</i> K.O. proximal tubular cell line. Disproportional cell
lineage differentiation is also observed in the patient group. The iPSC model
provides an opportunity to investigate the differences between normal and
disease cell differentiation in all the affected tissues, generate organoids,
and develop cell replacement therapies.
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/8258891 |
| Date | 13 August 2019 |
| Creators | Wen-Chieh Hsieh (6824807) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/UNDERSTANDING_AND_MANIPULATING_ENDOCYTOSIS-DEPENDENT_SIGNALING_CIRCUITS/8258891 |
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