Host-Derived BiP Overexpression Prolongs Productive Secretion and Enhances GLP-1–Fc Titer in CHO Cells

Chinese hamster ovary (CHO) cells are the principal platform for manufacturing recombinant biopharmaceuticals, but sustained production can exceed the protein-folding capacity of the endoplasmic reticulum (ER). Binding immunoglobulin protein (BiP/GRP78), encoded by Hspa5, is a major ER chaperone that supports folding and modulates unfolded protein response (UPR) signaling, yet its overexpression has been reported as beneficial or inhibitory depending on the product. Here, we stably overexpressed the Chinese hamster Hspa5 coding sequence in a CHO line producing a dulaglutide analogue comprising a modified GLP-1 peptide fused to human IgG4 Fc and compared BiP-overexpressing (DUL-BiP) cells with empty-vector (DUL-Neo) controls in fed-batch culture. At constant temperature, BiP overexpression did not alter viable cell density or viability, but DUL-BiP cells maintained higher late-stage cell-specific productivity, prolonged productive secretion by approximately two days, and reached a 40% higher final titer; under a temperature shift, maximal cell density decreased. Control cells induced endogenous BiP only at late culture stages, whereas DUL-BiP cells maintained an elevated BiP level from the start. Intracellular GLP-1–Fc did not accumulate progressively, and culture-associated changes in cleaved ATF6, eIF2α phosphorylation, and CHOP persisted in both lines. Constitutive host-derived BiP expression therefore enlarges the secretory reserve, sustaining late-stage secretion rather than increasing growth; the benefit depends on product-specific folding requirements.