Using variables to manipulate ranges for charts

Okay, so here is what I got:

ActiveChart.SeriesCollection(1).Values = "=PORTFOLIO!$C$54:$E$54"
ActiveChart.SeriesCollection(2).Values = "=PORTFOLIO!$C$56:$E$56"
ActiveChart.SeriesCollection(3).Values = "=PORTFOLIO!$C$58:$E$58"
ActiveChart.SeriesCollection(4).Values = "=PORTFOLIO!$C$60:$E$60"
ActiveChart.SeriesCollection(5).Values = "=PORTFOLIO!$C$62:$E$62"

Those E references are what I want to manipulate with variables. Optimally, I would like to have one cell on a sheet contain this reference. Then I would change the letter there, and then all of the charts would move to that specific reference (A, B, C, D, E, ...). The 5 series will always have the same letter reference. Can someone please help me out with the most ideal way to do this?

Thank you so much for bearing through my first post!