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Injury induced expression of caveolar proteins in human kidney tubules - role of megakaryoblastic leukemia 1

Krawczyk, Krzysztof M. LU ; Hansson, Jennifer LU ; Nilsson, Helén LU ; Krawczyk, Katarzyna K. LU ; Swärd, Karl LU and Johansson, Martin E. LU (2017) In BMC Nephrology 18(1).
Abstract

BACKGROUND: Caveolae are membrane invaginations measuring 50-100 nm. These organelles, composed of caveolin and cavin proteins, are important for cellular signaling and survival. Caveolae play incompletely defined roles in human kidneys. Induction of caveolin-1/CAV1 in diseased tubules has been described previously, but the responsible mechanism remains to be defined.

METHODS: Healthy and atrophying human kidneys were stained for caveolar proteins, (caveolin 1-3 and cavin 1-4) and examined by electron microscopy. Induction of caveolar proteins was studied in isolated proximal tubules and primary renal epithelial cells. These cells were challenged with hypoxia or H2O2. Primary tubular cells were also subjected to viral... (More)

BACKGROUND: Caveolae are membrane invaginations measuring 50-100 nm. These organelles, composed of caveolin and cavin proteins, are important for cellular signaling and survival. Caveolae play incompletely defined roles in human kidneys. Induction of caveolin-1/CAV1 in diseased tubules has been described previously, but the responsible mechanism remains to be defined.

METHODS: Healthy and atrophying human kidneys were stained for caveolar proteins, (caveolin 1-3 and cavin 1-4) and examined by electron microscopy. Induction of caveolar proteins was studied in isolated proximal tubules and primary renal epithelial cells. These cells were challenged with hypoxia or H2O2. Primary tubular cells were also subjected to viral overexpression of megakaryoblastic leukemia 1 (MKL1) and MKL1 inhibition by the MKL1 inhibitor CCG-1423. Putative coregulators of MKL1 activity were investigated by Western blotting for suppressor of cancer cell invasion (SCAI) and filamin A (FLNA). Finally, correlative bioinformatic studies of mRNA expression of caveolar proteins and MKL1 were performed.

RESULTS: In healthy kidneys, caveolar proteins were expressed by the parietal epithelial cells (PECs) of Bowman's capsule, endothelial cells and vascular smooth muscle. Electron microscopy confirmed caveolae in the PECs. No expression was seen in proximal tubules. In contrast, caveolar proteins were expressed in proximal tubules undergoing atrophy. Caveolar proteins were also induced in cultures of primary epithelial tubular cells. Expression was not enhanced by hypoxia or free radical stress (H2O2), but proved sensitive to inhibition of MKL1. Viral overexpression of MKL1 induced caveolin-1/CAV1, caveolin-2/CAV2 and SDPR/CAVIN2. In kidney tissue, the mRNA level of MKL1 correlated with the mRNA levels for caveolin-1/CAV1, caveolin-2/CAV2 and the archetypal MKL1 target tenascin C (TNC), as did the MKL1 coactivator FLNA. Costaining for TNC as readout for MKL1 activity demonstrated overlap with caveolin-1/CAV1 expression in PECs as well as in atrophic segments of proximal tubules.

CONCLUSIONS: Our findings support the view that MKL1 contributes to the expression of caveolar proteins in healthy kidneys and orchestrates the induction of tubular caveolar proteins in renal injury.

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organization
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Contribution to journal
publication status
published
subject
keywords
Caveolae, Caveolin, Cavin, FLNA, Kidney fibrosis, MKL1, SCAI
in
BMC Nephrology
volume
18
issue
1
publisher
BioMed Central
external identifiers
  • scopus:85049008947
ISSN
1471-2369
DOI
10.1186/s12882-017-0738-8
language
English
LU publication?
yes
id
8df18fac-e3a5-4fe4-808b-8189da4db37c
date added to LUP
2018-07-09 10:30:36
date last changed
2018-07-16 12:29:21
@article{8df18fac-e3a5-4fe4-808b-8189da4db37c,
  abstract     = {<p>BACKGROUND: Caveolae are membrane invaginations measuring 50-100 nm. These organelles, composed of caveolin and cavin proteins, are important for cellular signaling and survival. Caveolae play incompletely defined roles in human kidneys. Induction of caveolin-1/CAV1 in diseased tubules has been described previously, but the responsible mechanism remains to be defined.</p><p>METHODS: Healthy and atrophying human kidneys were stained for caveolar proteins, (caveolin 1-3 and cavin 1-4) and examined by electron microscopy. Induction of caveolar proteins was studied in isolated proximal tubules and primary renal epithelial cells. These cells were challenged with hypoxia or H2O2. Primary tubular cells were also subjected to viral overexpression of megakaryoblastic leukemia 1 (MKL1) and MKL1 inhibition by the MKL1 inhibitor CCG-1423. Putative coregulators of MKL1 activity were investigated by Western blotting for suppressor of cancer cell invasion (SCAI) and filamin A (FLNA). Finally, correlative bioinformatic studies of mRNA expression of caveolar proteins and MKL1 were performed.</p><p>RESULTS: In healthy kidneys, caveolar proteins were expressed by the parietal epithelial cells (PECs) of Bowman's capsule, endothelial cells and vascular smooth muscle. Electron microscopy confirmed caveolae in the PECs. No expression was seen in proximal tubules. In contrast, caveolar proteins were expressed in proximal tubules undergoing atrophy. Caveolar proteins were also induced in cultures of primary epithelial tubular cells. Expression was not enhanced by hypoxia or free radical stress (H2O2), but proved sensitive to inhibition of MKL1. Viral overexpression of MKL1 induced caveolin-1/CAV1, caveolin-2/CAV2 and SDPR/CAVIN2. In kidney tissue, the mRNA level of MKL1 correlated with the mRNA levels for caveolin-1/CAV1, caveolin-2/CAV2 and the archetypal MKL1 target tenascin C (TNC), as did the MKL1 coactivator FLNA. Costaining for TNC as readout for MKL1 activity demonstrated overlap with caveolin-1/CAV1 expression in PECs as well as in atrophic segments of proximal tubules.</p><p>CONCLUSIONS: Our findings support the view that MKL1 contributes to the expression of caveolar proteins in healthy kidneys and orchestrates the induction of tubular caveolar proteins in renal injury.</p>},
  articleno    = {320},
  author       = {Krawczyk, Krzysztof M. and Hansson, Jennifer and Nilsson, Helén and Krawczyk, Katarzyna K. and Swärd, Karl and Johansson, Martin E.},
  issn         = {1471-2369},
  keyword      = {Caveolae,Caveolin,Cavin,FLNA,Kidney fibrosis,MKL1,SCAI},
  language     = {eng},
  month        = {10},
  number       = {1},
  publisher    = {BioMed Central},
  series       = {BMC Nephrology},
  title        = {Injury induced expression of caveolar proteins in human kidney tubules - role of megakaryoblastic leukemia 1},
  url          = {http://dx.doi.org/10.1186/s12882-017-0738-8},
  volume       = {18},
  year         = {2017},
}