siRNA / miRNA gene silencing Human HeLa EPAS-1

I would like to regulate the expression of a gene and in order to do that, I have purchased specific siRNA. After optimizing my transfection protocol and using electroporation I have achieved a 60-70% reduction of the gene of interest. However, I cannot observe a significant reduction of mRNA expression but only a reduction of protein. What might be the problem? Could the problem be in my cell treatment method?

Get tips on using SIRT1 siRNA and shRNA Plasmids (h) to perform siRNA / miRNA gene silencing Human - PC3 (human prostate cancer cell line) SIRT1

Get tips on using Silencer select_ObR siRNA to perform siRNA / miRNA gene silencing Human - MCF-7 ObR(leptin receptor/LEPR)

Get tips on using Hs_TET3_2 FlexiTube siRNA to perform siRNA / miRNA gene silencing Human - HCT-116 TET3(TET methylcytosine dioxygenase 3)

Get tips on using esiRNA human PTPN3 (esiRNA1) to perform siRNA / miRNA gene silencing Human - A2780 PTPN3

Get tips on using ON-TARGETplus SMARTpool - Human to perform siRNA / miRNA gene silencing Human - U2OS DKC1

Get tips on using stealth siRNA GIRK1/KCNJ3 to perform siRNA / miRNA gene silencing Human - MDA-MB-453 GIRK1/KCNJ3

Get tips on using stealth siRNA GIRK1/KCNJ3 to perform siRNA / miRNA gene silencing Human - MDA-MB-231 GIRK1/KCNJ3

Get tips on using Dlx-2 siRNA (h) to perform siRNA / miRNA gene silencing Human - MDA-MB-231 DLX-2

Get tips on using Bcl-2 siRNA (h) to perform siRNA / miRNA gene silencing Human - MDA-MB-231 bcl-2