Bax inhibitor 1 increases cell adhesion through actin polymerization: involvement of calcium and actin binding.
Bax inhibitor 1 (BI-1), a transmembrane protein with Ca2+ channel-like activity, has antiapoptotic and anticancer activities. Cells overexpressing BI-1 demonstrated increased cell adhesion. Using a proteomics tool, we found that BI-1 interacted with gamma-actin via leucines 221 and 225 and could control actin polymerization and cell adhesion. Among BI-1-/- cells and cells transfected with BI-1 small interfering RNA (siRNA), levels of actin polymerization and cell adhesion were lower than those among BI-1+/+ cells and cells transfected with nonspecific siRNA. BI-1 acts as a leaky Ca2+ channel, but mutations of the actin binding sites (L221A, L225A, and L221A/L225A) did not change intra-endoplasmic reticulum Ca2+, although deleting the C-terminal motif (EKDKKKEKK) did. However, store-operated Ca2+ entry (SOCE) is activated in cells expressing BI-1 but not in cells expressing actin binding site mutants, even those with the intact C-terminal motif. Consistently, actin polymerization and cell adhesion were inhibited among all the mutant cells. Compared to BI-1+/+ cells, BI-1-/- cells inhibited SOCE, actin polymerization, and cell adhesion. Endogenous BI-1 knockdown cells showed a similar pattern. The C-terminal peptide of BI-1 (LMMLILAMNRKDKKKEKK) polymerized actin even after the deletion of four or six charged C-terminal residues. This indicates that the actin binding site containing L221 to D231 of BI-1 is responsible for actin interaction and that the C-terminal motif has only a supporting role. The intact C-terminal peptide also bundled actin and increased cell adhesion. The results of experiments with whole recombinant BI-1 reconstituted in membranes also coincide well with the results obtained with peptides. In summary, BI-1 increased actin polymerization and cell adhesion through Ca2+ regulation and actin interaction.
Lee
Geum-Hwa
GH
Department of Pharmacology and Cardiovascular Research Institute, Chonbuk National University, and Research Center for Pulmonary Disorder, Chonbuk National University Hospital, Jeonju, South Korea.
Ahn
Taeho
T
Kim
Do-Sung
DS
Park
Seoung Ju
SJ
Lee
Yong Chul
YC
Yoo
Wan Hee
WH
Jung
Sung Jun
SJ
Yang
Jae-Seong
JS
Kim
Sanguk
S
Muhlrad
Andras
A
Seo
Young-Rok
YR
Chae
Soo-Wan
SW
Kim
Hyung-Ryong
HR
Chae
Han-Jung
HJ
D000199:Actins / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D000970:Antineoplastic Agents / Q000378:metabolism; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002448:Cell Adhesion / Q000502:physiology*; D002460:Cell Line; D047630:Depsipeptides / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000378:metabolism; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D019284:Thapsigargin / Q000378:metabolism
D000199:Actins; D000970:Antineoplastic Agents; D051017:Apoptosis Regulatory Proteins; D047630:Depsipeptides; D004791:Enzyme Inhibitors; D008565:Membrane Proteins; D010455:Peptides; D034741:RNA, Small Interfering; C484209:TMBIM6 protein, human; C490015:Tmbim6 protein, mouse; C057531:jasplakinolide; D019284:Thapsigargin; D002118:Calcium