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© The Rockefeller University Press, 0021-9525/1997//999 $5.00
The Journal of Cell Biology, Volume 138, Number 5, , 1997 999-1008

Article

Kinesin- and Myosin-driven Steps of Vesicle Recruitment for Ca2+-regulated Exocytosis



Guo-Qiang Bi*, Robert L. Morris{ddagger}, Guochun Liao*, Janet M. Alderton*, Jonathan M. Scholey{ddagger}, and Richard A. Steinhardt*

* Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3200; and {ddagger} Section of Molecular and Cellular Biology, University of California, Davis, California 95616

Kinesin and myosin have been proposed to transport intracellular organelles and vesicles to the cell periphery in several cell systems. However, there has been little direct observation of the role of these motor proteins in the delivery of vesicles during regulated exocytosis in intact cells. Using a confocal microscope, we triggered local bursts of Ca2+-regulated exocytosis by wounding the cell membrane and visualized the resulting individual exocytotic events in real time. Different temporal phases of the exocytosis burst were distinguished by their sensitivities to reagents targeting different motor proteins. The function blocking antikinesin antibody SUK4 as well as the stalk-tail fragment of kinesin heavy chain specifically inhibited a slow phase, while butanedione monoxime, a myosin ATPase inhibitor, inhibited both the slow and fast phases. The blockage of Ca2+/calmodulin-dependent protein kinase II with autoinhibitory peptide also inhibited the slow and fast phases, consistent with disruption of a myosin-actin– dependent step of vesicle recruitment. Membrane resealing after wounding was also inhibited by these reagents. Our direct observations provide evidence that in intact living cells, kinesin and myosin motors may mediate two sequential transport steps that recruit vesicles to the release sites of Ca2+-regulated exocytosis, although the identity of the responsible myosin isoform is not yet known. They also indicate the existence of three semistable vesicular pools along this regulated membrane trafficking pathway. In addition, our results provide in vivo evidence for the cargo-binding function of the kinesin heavy chain tail domain.

Abbreviations used in this paper: BDM, 2,3-butanedione monoxime; CaM kinase II, Ca2+/calmodulin-dependent protein kinase II; KHC, kinesin heavy chain; KRP, kinesin-related protein.

Address all correspondence to Richard A. Steinhardt, Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720-3200. Tel.: (510) 642-3517. Fax: (510) 643-6791. E-mail: rick{at}mendel.berkeley.edu

Guo-Qiang Bi's current address is Department of Biology, University of California at San Diego, La Jolla, CA 92093-0357.


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