AAV VP1 unique region (VP1u) determines GPR108 dependence for AAV transduction of human airway epithelium and its rescue by Doxorubicin
rAAV2.5T was identified through directed evolution of an AAV capsid library in polarized human airway epithelium (HAE) cultured at an air-liquid interface (ALI). The capsid gene of rAAV2.5T is a chimera of the N-terminal unique region of AAV2 VP1 (VP1u) and the VP2 and VP3 regions of AAV5 with a single A581T substitution at the variable region (VR) VIII of the capsids. GPR108, a G protein-coupled receptor, is known as an essential host factor for the transduction of rAAV2 but not of rAAV5. Both AAV2 and AAV5 VP1u colocalized well with GPR108 and, to a lesser extent, with the trans-Golgi network (TGN). GPR108 knockout (KO) abolished rAAV2.5T transduction in both HeLa cells and HAE-ALI cultures. Remarkably, short-term treatment with doxorubicin (DOX) at 2 {micro}M completely restored transduction, indicating that DOX can compensate for the loss of GPR108 function. DOX enhanced rAAV2.5T transduction by 50-100-fold in wild-type HAE-ALI cultures and by over 300-fold in the GPR108-deficient cultures. Mechanistic studies demonstrated that this enhancement resulted from altered intracellular trafficking that promoted efficient vector nuclear import, rather than increased vector internalization, proteasome inhibition, or activation of the DNA damage response. Importantly, we identified that the N-terminal 15 amino acids of AAV2 VP1u as the primary determinant of rAAV2.5T dependence on GPR108 for transduction. Collectively, these findings demonstrate that productive transduction of rAAV2.5T in polarized HAE cultures depends on GPR108-mediated intracellular trafficking that limits efficient nuclear entry, and that DOX can relieve this constraint by promoting efficient vector import. SignificanceAAV2.5T is an airway-tropic vector with considerable promise for pulmonary gene therapy. We found that host factor GPR108 is required for rAAV2.5T trafficking from the TGN to the nucleus and that this step constitutes a major bottleneck to productive transduction in polarized HAE. In contrast, KIAA0319L (AAVR) plays a key role in AAV intracellular trafficking from the endosome to the TGN but not in internalization into polarized HAE during apical transduction. Transient treatment with low-dose doxorubicin (DOX, 2 {micro}M) enhanced rAAV2.5T transduction in HAE by 50-100-fold through a significant increase in vector nuclear import. Notably, DOX can overcome the transduction deficit caused by GPR108 deficiency, but not that caused by AAVR deficiency. Mechanistically, the N-terminal 15 amino acids of the VP1u confer GPR108 dependence during rAAV2.5T apical transduction of polarized HAE. DOX bypasses this requirement by promoting efficient nuclear import without affecting vector internalization, inhibiting proteasomes, or inducing DNA damage response.