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. 2007 Oct;13(4):511-22.
doi: 10.1016/j.devcel.2007.08.001.

Polarization-dependent selective transport to the apical membrane by KIF5B in MDCK cells

Fanny Jaulin  1 , Xiaoxiao Xue, Enrique Rodriguez-Boulan, Geri Kreitzer
Affiliations

Polarization-dependent selective transport to the apical membrane by KIF5B in MDCK cells

Fanny Jaulin et al. Dev Cell. 2007 Oct.

Abstract

Microtubule-based vesicular transport is well documented in epithelial cells, but the specific motors involved and their regulation during polarization are largely unknown. We demonstrate that KIF5B mediates post-Golgi transport of an apical protein in epithelial cells, but only after polarity has developed. Time-lapse imaging of EB1-GFP in polarized MDCK cells showed microtubule plus ends growing toward the apical membrane, implying that plus end-directed N-kinesins might be used to transport apical proteins. Indeed, time-lapse microscopy revealed that expression of a KIF5B dominant negative or microinjection of function-blocking KIF5 antibodies inhibited selectively post-Golgi transport of the apical marker, p75-GFP, after polarization of MDCK cells. Expression of other KIF dominant negatives did not alter p75-GFP trafficking. Immunoprecipitation experiments demonstrated an interaction between KIF5B and p75-GFP in polarized, but not in subconfluent, MDCK cells. Our results demonstrate that apical protein transport depends on selective microtubule motors and that epithelial cells switch kinesins for post-Golgi transport during acquisition of polarity.

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Figures

Figure 1
Figure 1. Rates of p75-GFP Emptying from the Golgi in Subconfluent and Polarized MDCK Cells
Subconfluent and polarized cells expressing p75-GFP were imaged by time-lapse microscopy for 3–4 hr after release of the Golgi block. For polarized cells, 3D image stacks were acquired at each time point. Golgi exit rates were calculated by measuring the ratio of Golgi:total p75-GFP fluorescence (Experimental Procedures). Data represent pooled results from three recordings for each data set shown. Error bars represent standard error of the mean (SEM).
Figure 2
Figure 2. Velocities of Post-Golgi Carriers Containing p75-GFP in Subconfluent and Polarized MDCK Cells
(A) Subconfluent and polarized cells expressing p75-GFP were imaged 15–45 min after release of the Golgi block by time-lapse confocal microscopy. Images were acquired at 1–2 s intervals for 2–5 min. Upper panels show selected sequential frames overlaid as time projections to illustrate vesicle paths. Arrows point to examples of tracked, post-Golgi carriers. (B and C) Individual frames (with time projections in bottom panels) tracking movement of two carriers in polarized cells. Time stamp in min:s. Corresponding movies are shown in Movies S1 and S2. (D) Histogram showing the distribution of velocities measured in subconfluent (n = 30) and polarized (n = 30) cells.
Figure 3
Figure 3. KIF Expression in Epithelial Cells
(A) Reverse transcription and PCR of human KIFs in A549, T84, and NHBE epithelial cells with KIF-specific primers. (B) Schematic representation of full-length KIF5B and KIF-specific tail constructs used as dominant-negative inhibitors.
Figure 4
Figure 4. Microtubule Plus Ends Are Oriented toward the Apical Membrane in Polarized MDCK Cells
(A and B) Polarized cells expressing EB1-GFP. (A) Sequential XY planes (1 μm steps) showing EB1-GFP in a single cell. (B) 3D reconstruction (90° view) of EB1-GFP in three cells. A time-lapse showing EB1-GFP on growing MTs with apically oriented plus ends can be found in Movie S3. Cycloheximide was added 60 min after injection of EB1-GFP cDNA (10 μg●ml−1) to prevent overexpression of exogenous protein. (C) Localization of endogenous EB1 and ZO-1 in polarized MDCK cells. Upper panel shows a maximum projection of sequential XY images. Lower panel shows a single orthogonal view of EB1 and ZO-1. Numerous EB1-labeled structures can be observed at and above the tight junction marker.
Figure 5
Figure 5. Polarization-Dependent, Selective Transport of p75-YFP by KIF5B
(A) Time-lapse images of polarized MDCK cells expressing p75-YFP, p75-YFP, and CFP-KIF5B-T or p75-YFP and HA-KIFC3-T. In all conditions, p75-YFP is found in the Golgi after the 20°C block (5 min 33°C). 4 hr later, (245 min 33°C), p75-YFP was delivered to the apical membrane in control and HA-KIFC3-expressing cells. By contrast, ~50% of p75-YFP remains in the Golgi in cells expressing CFP-KIF5B-T. Images show maximum XY projections of Z series. Lower panels show orthogonal views of injected cells at the end of each recording. Insets show corresponding CFP-KIF5B-T fluorescence and HA-KIFC3-T immunostained after the time lapse. Far right panels show p75-GFP in cells coinjected with H1 IgG at the start (5 min 33°C) and end (245 min 33°C) of a time lapse. (B) Polarized cells expressing p75-GFP and KIF5B-T or KIFC3-T were imaged by time-lapse microscopy for 3.5 hr after release of the Golgi block. p75-GFP exit from the Golgi was analyzed as described in Figure 1. KIFC3-T had no effect on emptying of p75-GFP from the Golgi. Error bars: SEM for KIF5B-T-, SD for KIFC3-T-expressing cells. (C) Post-Golgi transport of p75-YFP in subconfluent MDCK cells in the absence or presence of CFP-KIF5B-T. Expression of CFP-KIF5B-T does not inhibit transport of p75-YFP to the plasma membrane in subconfluent cells as compared with polarized cells. (D) p75-GFP associates with KIF5 in polarized but not subconfluent MDCK cells. KIF5 was present in approximately equal amounts in lysates used for IP (total lysate). Tubulin was blotted as a loading control.
Figure 6
Figure 6. KIF5B Is Not a General Motor for Transport to the Apical Membrane
Time-lapse images of polarized MDCK cells expressing GalT-CFP (control) or CFP-KIF5B-T and either GPI-YFP ([A] and [A′], control and CFP-KIF5B-T, respectively), BSEP-YFP (B), or prominin-YFP (C). All apical markers localized to the Golgi after a 20°C block and were delivered to the apical membrane in both control and KIF5B-T expressing 2–3 hr after release of the Golgi block. Images show maximum XY projections of Z series at indicated time points. Prominin appears as puncta in XY views because it associates with apical membrane protrusions. Orthagonal views of 3D image stacks illustrate apical distribution of these markers after release of the Golgi block. First and last time points are shown for GPI-YFP control and CFP-KIF5B-T recordings. First and last time points are shown for control BSEP-YFP and prominin-YFP recordings. Because CFP-KIF5B-T expression had no effect on accumulation of any marker in the Golgi during the 20°C, only the last frame from recordings of cells coexpressing CFP-KIF5B-T and BSEP-YFP or prominin-YFP is shown. Corresponding CFP-KIF5B-T fluorescence is shown in insets.
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