(A) UPR portrayed as a graded response that is proportional to the level of misfolded protein in the ER; the higher the level, the stronger the UPR. (Aa) Mutations causing ER accumulation of both PLP1 and DM-20 induce a strong UPR. (Ab) Mutations causing accumulation of PLP1 but not DM-20 induce a weak response.
(B) UPR portrayed as an off/on switch upon misfolded protein accumulation. (Ba) PLP1 and DM-20 accumulation induces the UPR. DM-20 is toxic and disrupts cell survival pathways (?). (Bb) Accumulation of only PLP1 in the ER induces the UPR but does not affect cell survival pathways.