CCND1 and esophageal squamous cell carcinoma: However, when the MEK/ERK pathway in SRGN-overexpressing ESCC cells was suppressed by treatment with trametinib, leading to downregulation of known downstream effectors of MEK/ERK pathway such as CD44, c-Myc, and CCND1, there were no significant changes in the mRNA expression of MDK (Figure 4B), inferring that MDK is not a direct downstream effector of the MEK/ERK pathway.