eprintid: 17515
rev_number: 14
eprint_status: archive
userid: 1405
dir: disk0/00/01/75/15
datestamp: 2014-10-21 13:35:18
lastmod: 2014-10-30 11:34:05
status_changed: 2014-10-21 13:35:18
type: doctoralThesis
metadata_visibility: show
creators_name: Chung, Shan-Hua
title: Mechanisms of STIM1-mediated endoplasmic reticulum-plasma membrane (ER-PM) contact formation
subjects: ddc-500
subjects: ddc-570
divisions: i-140001
adv_faculty: af-14
abstract: The coupling of endoplasmic reticulum (ER) and plasma membrane (PM) is crucial for
calcium (Ca2+) homeostasis. STIM1 and STIM2 are type I membrane proteins of the ER and
function as Ca2+ sensors in a process known as store-operated calcium entry (SOCE). They
sense a drop in luminal Ca2+ concentration and undergo conformational changes and
oligomerization. The active oligomerized STIM proteins translocate to ER-PM contact sites,
where they bind to phosphoinositides (PIPs) at the inner leaflet of the PM via their lysine (K)-
rich domains and activate Orai1, a pore-forming Ca2+ release-activated Ca2+ (CRAC)
channel subunit in the PM.
I found that STIM2, but not STIM1, contains a di-lysine ER-retention signal. This
signal restricts the function of STIM2 as Ca2+ sensor to the ER while STIM1 can reach the
PM via the classical secretary pathway. The intracellular distribution of STIM1 is regulated in
a cell-cycle-dependent manner with cell surface expression of STIM1 during mitosis.
Efficient retention of STIM1 in the ER during interphase depends on its K-rich domain and a
di-arginine ER retention signal. SOCE enhances ER retention, suggesting that trafficking of
STIM1 is regulated and this regulation contributes to STIM1’s role as multifunctional
component in Ca2+-signaling.
In contrast to mitotic cells, interphase cells retain most of their STIM1 intracellularly.
Under resting condition, the ER-resident STIMs are preferentially located in PI(4,5)P2
containing preexisting ER-PM contact sites, which are expanded upon ER Ca2+ depletion.
The lipid-binding, K-rich domains are required to localize STIM proteins in preexisting ERPM
contact sites. Moreover, STIM2 recruits ER more efficiently to the PM. This is consistent
with the fact that STIM2 has higher lipid-binding affinity and lower activation threshold than
STIM1 and that STIM2 functions as a regulator of basal Ca2+ homeostasis.
Finally, I studied the role of microtubules in ER-PM contact site formation. I observed
that STIM1 aligns along microtubules. Alignment of STIM proteins with microtubules is a
conserved process. In addition to accumulation of STIM1 at microtubule plus ends, STIM1
moves along microtubules in an EB-1-independent manner. I identified two EB-1-
independent microtubule-binding sites located within the C-terminus of STIM1 and found
that oligomerization increases the EB-1-independent microtubule-binding affinity of STIM1.
However, the physiological function of this EB1-independent microtubule binding activity
remains elusive.
date: 2014
id_scheme: DOI
id_number: 10.11588/heidok.00017515
ppn_swb: 1659402468
own_urn: urn:nbn:de:bsz:16-heidok-175153
date_accepted: 2014-09-25
advisor: HASH(0x55a9a62f9138)
language: eng
bibsort: CHUNGSHANHMECHANISMS2014
full_text_status: public
place_of_pub: Heidelberg
citation:   Chung, Shan-Hua  (2014) Mechanisms of STIM1-mediated endoplasmic reticulum-plasma membrane (ER-PM) contact formation.  [Dissertation]     
document_url: https://archiv.ub.uni-heidelberg.de/volltextserver/17515/1/thesis_final_20140620.pdf