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Review
. 2013 Nov 1;319(18):2759-69.
doi: 10.1016/j.yexcr.2013.08.008. Epub 2013 Aug 13.

Clathrin-independent endocytosis: a cargo-centric view

Lymarie Maldonado-Báez  1 , Chad Williamson, Julie G Donaldson
Affiliations
Review

Clathrin-independent endocytosis: a cargo-centric view

Lymarie Maldonado-Báez et al. Exp Cell Res. .

Abstract

Clathrin-independent endocytosis occurs in all cells and interest in this mode of cellular entry has grown. Although this form of endocytosis was first described for entry of bacterial toxins, here we focus our attention on the endogenous cell surface "cargo" proteins that enter cells by this mechanism. The cargo proteins entering by this mechanism are varied and include nutrient transporters, ion channels, cell adhesion molecules and proteins associated with the immune system. Despite the apparent lack of selection at the cell surface, we provide some examples of specific sorting of these cargo proteins after entry, leading to distinct itineraries and cellular fates.

Keywords: Cell adhesion molecules; Clathrin-independent endocytosis; Endocytosis; Ion channels; Nutrient transporters; Plasma membrane protein; Protein sorting.

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Figures

Figure 1
Figure 1
General model for CIE and CME and subsequent membrane trafficking. Itinerary followed by CIE and CME cargo proteins. CIE cargo (red and blue bars) enter separately from CME cargo (black bars) but then enter the common Sorting Endosome (SE) where cargo can be sorted and moved to different destinations. Some CIE cargo proteins (blue bars) take the Direct recycling pathway (via tubules) back to the PM while other CIE cargo proteins (red bars) take the Indirect pathway (via the Endocytic Recycling Compartment (ERC) and then tubules) back to the PM. Some of the Arf and Rab regulators are shown. Cargo entering by CME (black bars) can recycle back to the PM via Rab5 sorting endosome or Rab11 ERC. CME cargo and CIE cargo that take the indirect route (Red bars) also trafficking to Lamp1-positive late endosomes/lysosomes for degradation.
Figure 2
Figure 2
Factors influencing the sorting and trafficking of cargo on sorting endosomes. A closer look at the sorting events that occur on the sorting endosome (SE). Cargo that is ubiquitinylated (green triangle) by MARCH or other E3 ligases gets sorted into invaginating membrane forming intralumenal vesicles or multi-vesicular bodies (MVB). Deubiquitinating enzymes (DUBS) remove ubiquitin allowing cargo to escape degradation. Hook1, Rab22 and microtubules facilitate the sorting of Direct CIE cargo (blue bars) into recycling tubules. Indirect CIE cargo (red bars) is routed back to PM via ERC and tubules.
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