Since ABC transporter family utilize the energy of ATP hydrolysis to transport various small molecules across cellular membranes, it seems that ABC transporters may mainly mediate the efflux of erythromycin rather than import molecules associated with erythromycin synthesis.
ABC transporters, for example, Pgp membrane efflux pumps, are expressed in normal tissues including intestinal epithelia, liver, renal tubules, and lung, where they mediate the efflux of toxins and drugs (Han and Zhang, 2004; Leslie et al, 2005).
In addition, CSCs typically overexpress cell membrane ATP-binding cassette (ABC) drug transporters such as P-gp, which mediate the efflux of a large number of cytotoxic compounds, including doxorubicin.
Upon exposure to sublethal oxidative stress, cells attempt to restore redox homeostasis through the upregulated production of antioxidants, detoxifying enzymes, as well as phase III drug transporters to mediate the efflux of potentially harmful oxidation products [ 86, 87].
MDR1, BCRP and MRP2 mediate the efflux of a broad range of substrates including a large variety of drugs and chemotherapy agents for which they share an overlap of substrate specificity (Nies and Keppler 2007; Polgar et al. 2008; Cascorbi 2011).
Although ABCB1, ABCC1 and ABCG2 are all implicated in the resistance to doxorubicin [ 19], the lack of cross-resistance to doxorubicin in MCF-7TXT cells suggests that the ABCB1 overexpression alone may not efficiently mediate the efflux of doxorubicin in this selected MCF-7 cell line.
The CmeABC multidrug efflux pump, which belongs to the resistance-nodulation-division (RND) family, recognizes and extrudes a broad range of antimicrobial agents and is essential for Campylobacter jejuni colonization of the animal intestinal tract by mediating the efflux of bile acids.
This Na+ extrusion system, however, seems not to depend on the plasma membrane Na+/K+-ATPase that mediates the efflux 3Na+ and the influx 2 K+, which is ubiquitous in animal cells (Jeschke [1984]).
ASCT1 not only mediates the efflux of glutamate from the neuron into the synaptic junction via Calcium-independent release, but also mediates the efflux of L-serine from glial cells and its uptake by neurons [ 17- 19].
In the presence of bile salts, ABCB4 located in nonraft membranes mediates the efflux of phospholipids, preferentially phosphatidylcholine.
ABCA1 is a lipid transporter that mediates the efflux of cellular cholesterol to lipid-free apolipoprotein A-I [ 49].
