Cargo and Dynamin Regulate Clathrin-Coated Pit Maturation

Constitutive CME is saturable.

“Previously, it has been reported that constitutive CME is saturable (Warren et al., 1997, 1998; Loerke et al., 2009).”

We previously identified an endocytic restriction/checkpoint and provided evidence that progression beyond the checkpoint (i.e., CCP maturation efficiency) was enhanced by TfnR overexpression in a manner dependent on AP2 adaptors.

“We previously identified an endocytic restriction/checkpoint and provided evidence that progression beyond the checkpoint (i.e., CCP maturation efficiency) was enhanced by TfnR overexpression in a manner dependent on AP2 adaptors (Loerke et al., 2009).”

Overexpression of TfnR, a constitutively internalized AP2-dependent cargo, increased the efficiency of CCP maturation by increasing the contribution of productive CCPs at the expense of abortive species without affecting the rate of CCP maturation (lifetimes of productive CCPs).

“Previously, we showed that overexpression of TfnR, a constitutively internalized, AP2-dependent cargo, increased the efficiency of CCP maturation by increasing the contribution of productive CCPs at the expense of abortive species without affecting the rate of CCP maturation, i.e., the lifetimes of productive CCPs (Loerke et al., 2009).”

Incorporation of transferrin receptor/AP2 into CCPs increases the efficiency of CCP maturation without affecting CCP density or CCP maturation rate.

“The incorporation of certain cargo/adaptor protein complexes (i.e., transferrin receptor/AP2) into CCPs increases the efficiency of CCP maturation without affecting CCP density or CCP maturation rate (Loerke et al., 2009; Mettlen et al., 2009).”

Nonterminal events are more frequent in HeLa cells, which express relatively high levels of Dab2 and cargo.

“This idea is further supported by the observation that nonterminal events are more frequent in HeLa cells (Ehrlich et al., 2004; Merrifield et al., 2005; Loerke et al., 2009), which express relatively high levels of Dab2 and cargo (Maurer and Cooper, 2006; unpublished data).”

Three CCP subpopulations exist: early abortive, late abortive, and productive CCPs.

“Recently, based on lifetime decomposition, we identified three CCP subpopulations, termed early abortive, late abortive, and productive CCPs (Loerke et al., 2009).”

TfnR overexpression did not affect AP2 distribution.

“In contrast to TfnR overexpression, which did not affect AP2 distribution (Loerke et al., 2009)”

Even constitutively internalized cargo and their adaptors can regulate multiple aspects of CCP maturation.

“Together with our previous results (Loerke et al., 2009), we establish that even constitutively internalized cargo and their adaptors can regulate multiple aspects of CCP maturation”