HSPA5 and ovarian cancer: Induces the expression of GRP78, p‐PERK, p‐eIF2α, ATF‐4, CHOP, and DR5. In gefitinib‐resistant ovarian cancer cells, 6‐shogaol upregulates N‐cadherin, vimentin, Slug, and Snail, while downregulated E‐cadherin overcoming gefitinib resistance